TMVP derivation

ABSTRACT

A video processing method includes deriving multiple temporal motion vector prediction (TMVP) candidates for a video block in a current picture based on multiple blocks associated with a second block in one or more pictures that are temporally co-located with the current picture, wherein the current picture is excluded from the one or more pictures, and the second block is temporally collocated with the video block, wherein the second block has a same size as the video block, and wherein a relative position of the second block to a top-left corner of a second picture of the one or more pictures is same as that of the video block to a top-left corner of the current picture; adding the multiple TMVP candidates to a motion candidate list associated with the video block; and performing a conversion between the video block and a bitstream.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/IB2019/055546, filed on Jul. 1, 2019, which claims the priority toand benefits of International Patent Application No. PCT/CN2018/093656,filed on Jun. 29, 2018. The entire disclosures of the aforementionedapplications are incorporated by reference as part of the disclosure ofthis application in their entireties.

TECHNICAL FIELD

This patent document relates to video processing techniques, devices andsystems.

BACKGROUND

In spite of the advances in video compression, digital video stillaccounts for the largest bandwidth use on the internet and other digitalcommunication networks. As the number of connected user devices capableof receiving and displaying video increases, it is expected that thebandwidth demand for digital video usage will continue to grow.

SUMMARY

This document discloses methods, systems, and devices for encoding anddecoding digital video using a merge list of motion vectors.

In one example aspect, a video encoding method includes splitting ablock of video data into M sub-blocks according to a partitionstructure, coding a first subset of the M sub-blocks according to commonmotion information; and coding a second subset of the M sub-blocksaccording to motion information that is different than the common motioninformation for the first subset.

In another example aspect, a video decoding method includes parsing thevideo bitstream and reconstructing video pictures based on the parsedvideo bitstream. The video bitstream includes at least a block of videodata that is split into M sub-blocks according to a partition structure.M is an integer greater than 1. A first subset of the M sub-blocks iscoded according to common motion information and a second subset of theM sub-blocks is coded according to motion information different than thecommon motion information.

In another example aspect, a video processing method includes deriving amerge candidate list of a child node based on a plurality of neighboringblocks of a parent node of the child node. The parent node represents aunit of video data and is split into multiple child nodes according to apartition structure. The multiple child nodes include the child node andat least another child node adjacent to the child node. The method alsoincludes performing a conversion between the unit of video data and thevideo bitstream.

In another example aspect, a video processing method includesdetermining a dimension of a motion estimation region based on a codingcharacteristic of a video block. The method also includes performing aconversion between the video block and a video bitstream based on themotion estimation region. The motion estimation region represents aportion of a video frame that includes the video block such that amotion vector candidate list is independently derived by checkingwhether a candidate block is located in the merge estimation region.

In another example aspect, a video processing method includes derivingmultiple temporal motion vector prediction (TMVP) candidates for a videoblock in a current picture based on multiple blocks in one or morepictures that are temporally co-located with the current picture. Thecurrent picture is excluded from the one or more pictures. The methodalso includes adding the multiple TMVP candidates to a motion candidatelist associated with the video block and performing a conversion betweenthe video block and a bitstream.

In another example aspect, a video processing method includesgenerating, for a conversion between a video block in a video pictureand a bitstream representation of the video block, a list of mergecandidates for the video block. The list of merge candidates includes atleast a first merge candidate that is a virtual merge candidate derivedby modifying a motion vector and/or a reference picture of a secondmerge candidate. The method also includes performing, using the list ofmerge candidates, the conversion between the video block and the videobitstream.

In another example aspect, a video processing includes determining, fora sub-block of a current video block, a sub-block motion candidate basedon a first block identified by a motion vector of a spatial mergecandidate of the current video block and a relative position between thecurrent video block and a second block wherein the spatial mergecandidate is from.

The method also includes performing, using the sub-block motioncandidate, a conversion between the current video block and the videobitstream.

In another example aspect, a video decoding method is disclosed. Themethod includes decoding a video bitstream in which at least one videoblock is represented using a motion estimation region that is dependenton a coding characteristic of the video block, and reconstructing, fromthe parsing, a decoded version of the video block, wherein the motionestimation region represents a portion of a video frame that includesthe video block such that a motion vector merge candidate lists can beindependently derived by checking whether a candidate block is locatedin that merge estimation region.

In another example aspect, another video decoding method is disclosed.The method includes generating, for a motion compensated video block ina video bitstream, a list of merge candidates, according to a firstrule, determining, using a second rule, a current motion informationfrom the list of merge candidates, and reconstructing the video blockbased on the current motion information.

In yet another aspect, a video decoding method is disclosed. The methodincludes generating, for a video block in a video bitstream, a list ofmerge candidates, according to a first rule, extending, using a secondrule, the list of merge candidates to an extended list of mergecandidates that includes additional merge candidates, and reconstructingthe video block using the extended list of merge candidates.

In another example aspect, a method of decoding video bitstream isdisclosed. The method includes parsing the video bitstream, andreconstructing video pictures from the parsing. The video bitstreamincludes at least one block indicated by a parent node that is splitinto M sub-blocks indicated by child nodes wherein mode information ofeach sub-block is coded separately and the M sub-blocks are not furthersplit, and M is an integer greater than 1, and wherein not all of the Msub-blocks share same motion information.

In one example aspect, a video encoding method includes derivingmultiple temporal motion vector prediction (TMVP) candidates for a videoblock in a current picture based on multiple blocks associated with asecond block in one or more pictures that are temporally co-located withthe current picture, wherein the current picture is excluded from theone or more pictures, and the second block is temporally collocated withthe video block, wherein the second block has a same size as the videoblock, and wherein a relative position of the second block to a top-leftcorner of a second picture of the one or more pictures is same as thatof the video block to a top-left corner of the current picture; addingthe multiple TMVP candidates to a motion candidate list associated withthe video block; and performing a conversion between the video block anda bitstream.

In yet another example aspect, a video decoding apparatus thatimplements one of the above-described methods is disclosed.

In yet another example aspect, a video encoder device that implementsone of the above described method is disclosed.

In yet another representative aspect, the various techniques describedherein may be embodied as a computer program product stored on anon-transitory computer readable media.

The computer program product includes program code for carrying out themethods described herein.

The details of one or more implementations are set forth in theaccompanying attachments, the drawings, and the description below. Otherfeatures will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a video encoderimplementation

FIG. 2 illustrates macroblock partitioning in the H.264 video codingstandard.

FIG. 3 illustrates an example of splitting coding blocks (CB) intoprediction blocks (PBs).

FIG. 4 illustrates an example implementation for subdivision of a codingtree block (CTB) into CBs and transform block (TBs). Solid linesindicate CB boundaries and dotted lines indicate TB boundaries,including an example CTB with its partitioning, and a correspondingquadtree.

FIG. 5 shows an example of a Quad Tree Binary Tree (QTBT) structure forpartitioning video data.

FIG. 6 shows an example of video block partitioning.

FIG. 7 shows an example of quad-tree partitioning.

FIG. 8 shows an example of tree-type signaling.

FIG. 9 shows an example of a derivation process for merge candidate listconstruction.

FIG. 10 shows example positions of spatial merge candidates.

FIG. 11 shows examples of candidate pairs considered for redundancycheck of spatial merge candidates.

FIG. 12 shows examples of positions for the second PU of N×2N and 2N×Npartitions.

FIG. 13 illustrates example motion vector scaling for temporal mergecandidates.

FIG. 14 shows candidate positions for temporal merge candidates, andtheir co-located picture.

FIG. 15 shows an example of a combined bi-predictive merge candidate.

FIG. 16 shows an example of a derivation process for motion vectorprediction candidates.

FIG. 17 shows an example of motion vector scaling for spatial motionvector candidates.

FIG. 18 shows an example Alternative Temporal Motion Vector Prediction(ATMVP for motion prediction of a coding unit (CU).

FIG. 19 pictorially depicts an example of identification of a sourceblock and a source picture.

FIG. 20 shows an example of one CU with four sub-blocks and neighboringblocks.

FIG. 21 illustrates an example of bilateral matching.

FIG. 22 illustrates an example of template matching.

FIG. 23 depicts an example of unilateral Motion Estimation (ME) in FrameRate Up Conversion (FRUC).

FIG. 24 shows an example of Decoder-Side Motion Vector Refinement (DMVR)based on bilateral template matching.

FIG. 25 illustrates an example of source block identification.

FIG. 26A illustrates an example of a second CU under an AsymmetricBinary Tree (ABT) partition structure in accordance with one or moreembodiments of the disclosed technology.

FIG. 26B illustrates an example of CUs under a Ternary Tree (TT)partition in accordance with one or more embodiments of the disclosedtechnology.

FIG. 26C illustrates an example of multiple blocks for Temporal MotionVector Prediction (TMVP) candidate derivation outside the col-locatedblock in accordance with one or more embodiments of the disclosedtechnology.

FIG. 26D illustrates an example of multiple blocks for TMVP candidatederivation within the col-located Coding Tree Unit (CTU) in accordancewith one or more embodiments of the disclosed technology.

FIG. 26E illustrates an example of multiple blocks for TMVP candidatederivation outside the col-located block in accordance with one or moreembodiments of the disclosed technology.

FIG. 27 is a block diagram of an example of a hardware platform forimplementing a visual media decoding or a visual media encodingtechnique described in the present document.

FIG. 28 is a flowchart for an example method of video bitstreamprocessing.

FIG. 29 is a flowchart for another example method of video bitstreamprocessing.

FIG. 30 is a flowchart for another example method of video bitstreamprocessing.

FIG. 31 is a flowchart representation for a video encoding method inaccordance with the disclosed technology.

FIG. 32 is a flowchart representation for a video decoding method inaccordance with the disclosed technology.

FIG. 33 is a flowchart representation of a video processing method inaccordance with the disclosed technology.

FIG. 34 is a flowchart representation of another video processing methodin accordance with the disclosed technology.

FIG. 35 is a flowchart representation of another video processing methodin accordance with the disclosed technology.

FIG. 36 is a flowchart representation of another video processing methodin accordance with the disclosed technology.

FIG. 37 is a flowchart representation of yet another video processingmethod in accordance with the disclosed technology.

DETAILED DESCRIPTION

To improve compression ratio of avideo, researchers are continuallylooking for new techniques by which to encode video.

1. Introduction

This patent document describes techniques related to video codingtechnologies. Specifically, it describes techniques related to mergemode in video coding. The disclosed techniques can be applied to theexisting video coding standard like High Efficiency Video Coding (HEVC),or the standard Versatile Video Coding (VVC) to be finalized. It may bealso applicable to future video coding standards or video codec.

Brief Discussion

Video coding standards have evolved primarily through the development ofthe well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 andH.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Anexample of a typical HEVC encoder framework is depicted in FIG. 1 .

2.1 Partition Structure

2.1.1 Partition Tree Structure in H.264/AVC

The core of the coding layer in previous standards was the macroblock,containing a 16×16 block of luma samples and, in the usual case of 4:2:0color sampling, two corresponding 8×8 blocks of chroma samples.

An intra-coded block uses spatial prediction to exploit spatialcorrelation among pixels. Two partitions are defined: 16×16 and 4×4.

An inter-coded block uses temporal prediction, instead of spatialprediction, by estimating motion among pictures. Motion can be estimatedindependently for either 16×16 macroblock or any of its sub-macroblockpartitions: 16×8, 8×16, 8×8, 8×4, 4×8, 4×4 (see FIG. 2 ). Only onemotion vector (MV) per sub-macroblock partition is allowed.

2.1.2 Partition Tree Structure in HEVC

In HEVC, a CTU is split into CUs by using a quadtree structure denotedas coding tree to adapt to various local characteristics. The decisionwhether to code a picture area using inter-picture (temporal) orintra-picture (spatial) prediction is made at the CU level. Each CU canbe further split into one, two or four PUs according to the PU splittingtype. Inside one PU, the same prediction process is applied and therelevant information is transmitted to the decoder on a PU basis. Afterobtaining the residual block by applying the prediction process based onthe PU splitting type, a CU can be partitioned into transform units(TUs) according to another quadtree structure similar to the coding treefor the CU. One of key feature of the HEVC structure is that it has themultiple partition conceptions including CU, PU, and TU.

The various features involved in hybrid video coding using HEVC arehighlighted as follows.

1) Coding tree units and coding tree block (CTB) structure: Theanalogous structure in HEVC is the coding tree unit (CTU), which has asize selected by the encoder and can be larger than a traditionalmacroblock. The CTU consists of a luma CTB and the corresponding chromaCTBs and syntax elements. The size L×L of a luma CTB can be chosen asL=16, 32, or 64 samples, with the larger sizes typically enabling bettercompression. HEVC then supports a partitioning of the CTBs into smallerblocks using a tree structure and quadtree-like signaling.

2) Coding units (CUs) and coding blocks (CBs): The quadtree syntax ofthe CTU specifies the size and positions of its luma and chroma CBs. Theroot of the quadtree is associated with the CTU. Hence, the size of theluma CTB is the largest supported size for a luma CB. The splitting of aCTU into luma and chroma CBs is signaled jointly. One luma CB andordinarily two chroma CBs, together with associated syntax, form acoding unit (CU). A CTB may contain only one CU or may be split to formmultiple CUs, and each CU has an associated partitioning into predictionunits (PUs) and a tree of transform units (TUs).

3) Prediction units (PUs) and prediction blocks (PBs): The decisionwhether to code a picture area using inter picture or intra pictureprediction is made at the CU level. A PU partitioning structure has itsroot at the CU level. Depending on the basic prediction-type decision,the luma and chroma CBs can then be further split in size and predictedfrom luma and chroma prediction blocks (PBs). HEVC supports variable PBsizes from 64×64 down to 4×4 samples. FIG. 3 shows examples of allowedPBs for a M×M CU.

4) Transform Units (TUs) and transform blocks (TBs): The predictionresidual is coded using block transforms. A TU tree structure has itsroot at the CU level. The luma CB residual may be identical to the lumaTB or may be further split into smaller luma TB s. The same applies tothe chroma TBs. Integer basis functions similar to those of a discretecosine transform (DCT) are defined for the square TB sizes 4×4, 8×8,16×16, and 32×32. For the 4×4 transform of luma intra picture predictionresiduals, an integer transform derived from a form of discrete sinetransform (DST) is alternatively specified.

FIG. 4 shows an example of a subdivision of a CTB into CBs [andtransform block (TBs)]. Solid lines indicate CB borders and dotted linesindicate TB borders. (a) CTB with its partitioning. (b) correspondingquadtree.

2.1.2.1 Tree-Structured Partitioning into Transform Blocks and Units

For residual coding, a CB can be recursively partitioned into transformblocks (TBs). The partitioning is signaled by a residual quadtree. Onlysquare CB and TB partitioning is specified, where a block can berecursively split into quadrants, as illustrated in FIG. 4 . For a givenluma CB of size M×M, a flag signals whether it is split into four blocksof size M/2×M/2. If further splitting is possible, as signaled by amaximum depth of the residual quadtree indicated in the SequenceParameter Set (SPS), each quadrant is assigned a flag that indicateswhether it is split into four quadrants. The leaf node blocks resultingfrom the residual quadtree are the transform blocks that are furtherprocessed by transform coding. The encoder indicates the maximum andminimum luma TB sizes that it will use. Splitting is implicit when theCB size is larger than the maximum TB size. Not splitting is implicitwhen splitting would result in a luma TB size smaller than the indicatedminimum. The chroma TB size is half the luma TB size in each dimension,except when the luma TB size is 4×4, in which case a single 4×4 chromaTB is used for the region covered by four 4×4 luma TBs. In the case ofintra-picture-predicted CUs, the decoded samples of thenearest-neighboring TBs (within or outside the CB) are used as referencedata for intra picture prediction.

In contrast to previous standards, the HEVC design allows a TB to spanacross multiple PBs for inter-picture predicted CUs to maximize thepotential coding efficiency benefits of the quadtree-structured TBpartitioning.

2.1.2.2 Parent and Child Nodes

A CTB is divided according to a quad-tree structure, the nodes of whichare coding units. The plurality of nodes in a quad-tree structureincludes leaf nodes and non-leaf nodes. The leaf nodes have no childnodes in the tree structure (e.g., the leaf nodes are not furthersplit). The non-leaf nodes include a root node of the tree structure.The root node corresponds to an initial video block of the video data(e.g., a CTB). For each respective non-root node of the plurality ofnodes, the respective non-root node corresponds to a video block that isa sub-block of a video block corresponding to a parent node in the treestructure of the respective non-root node. Each respective non-leaf nodeof the plurality of non-leaf nodes has one or more child nodes in thetree structure.

2.1.3 Quadtree Plus Binary Tree Block Structure with Larger CTUs inJoint Exploration Model (JEM)

To explore the future video coding technologies beyond HEVC, Joint VideoExploration Team (JVET) was founded by VCEG and MPEG jointly in 2015.Since then, many new methods have been adopted by JVET and put into thereference software named Joint Exploration Model (JEM).

2.1.3.1 QTBT Block Partitioning Structure

Different from HEVC, the QTBT structure removes the concepts of multiplepartition types. For example, the QTBT structure removes the separationof the CU, PU and TU concepts, and supports more flexibility for CUpartition shapes. In the QTBT block structure, a CU can have either asquare or rectangular shape. As shown in FIG. 5 , a coding tree unit(CTU) is first partitioned by a quadtree structure. The quadtree leafnodes are further partitioned by a binary tree structure. There are twosplitting types—symmetric horizontal splitting and symmetric verticalsplitting—in the binary tree splitting. The binary tree leaf nodes arecalled coding units (CUs), and that segmentation is used for predictionand transform processing without any further partitioning. This meansthat the CU, PU and TU have the same block size in the QTBT coding blockstructure. In the JEM, a CU sometimes consists of coding blocks (CBs) ofdifferent colour components, e.g. one CU contains one luma CB and twochroma CBs in the case of predictive (P) and Bi-predictive (B) slices ofthe 4:2:0 chroma format and sometimes consists of a CB of a singlecomponent, e.g., one CU contains only one luma CB or just two chroma CBsin the case of I slices.

The following parameters are defined for the QTBT partitioning scheme.

-   -   CTU size: the root node size of a quadtree, the same concept as        in HEVC    -   MinQTSize: the minimally allowed quadtree leaf node size    -   MaxBTSize: the maximally allowed binary tree root node size    -   MaxBTDepth: the maximally allowed binary tree depth    -   MinBTSize: the minimally allowed binary tree leaf node size

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64,the MinBTSize (for both width and height) is set as 4×4, and theMaxBTDepth is set as 4. The quadtree partitioning is applied to the CTUfirst to generate quadtree leaf nodes. The quadtree leaf nodes may havea size from 16×16 (e.g., the MinQTSize) to 128×128 (e.g., the CTU size).If the leaf quadtree node is 128×128, it will not be further split bythe binary tree since the size exceeds the MaxBTSize (e.g., 64×64).Otherwise, the leaf quadtree node could be further partitioned by thebinary tree. Therefore, the quadtree leaf node is also the root node forthe binary tree and it has the binary tree depth as 0. When the binarytree depth reaches MaxBTDepth (e.g., 4), no further splitting isconsidered. When the binary tree node has width equal to MinBTSize(e.g., 4), no further horizontal splitting is considered. Similarly,when the binary tree node has height equal to MinBTSize, no furthervertical splitting is considered. The leaf nodes of the binary tree arefurther processed by prediction and transform processing without anyfurther partitioning. In the JEM, the maximum CTU size is 256×256 lumasamples.

The left part of FIG. 5 illustrates an example of block partitioning byusing QTBT, and the right part of FIG. 5 illustrates the correspondingtree representation. The solid lines indicate quadtree splitting anddotted lines indicate binary tree splitting. In each splitting (e.g.,non-leaf) node of the binary tree, one flag is signalled to indicatewhich splitting type (e.g., horizontal or vertical) is used, where 0indicates horizontal splitting and 1 indicates vertical splitting. Forthe quadtree splitting, there is no need to indicate the splitting typesince quadtree splitting always splits a block both horizontally andvertically to produce 4 sub-blocks with an equal size.

In addition, the QTBT scheme supports the ability for the luma andchroma to have a separate QTBT structure. Currently, for P and B slices,the luma and chroma CTBs in one CTU share the same QTBT structure.However, for Intra-coded (I) slices, the luma CTB is partitioned intoCUs by a QTBT structure, and the chroma CTBs are partitioned into chromaCUs by another QTBT structure. This means that a CU in an I sliceconsists of a coding block of the luma component or coding blocks of twochroma components, and a CU in a P or B slice consists of coding blocksof all three colour components.

In HEVC, inter prediction for small blocks is restricted to reduce thememory access of motion compensation, such that bi-prediction is notsupported for 4×8 and 8×4 blocks, and inter prediction is not supportedfor 4x4 blocks. In the QTBT of the JEM, these restrictions are removed.

2.1.4 Ternary-Tree for Versatile Video Coding (VVC)

FIG. 6 illustrates examples of: (a) a quad-tree partitioning, (b) avertical binary-tree partitioning (c) a horizontal binary-treepartitioning (d) a vertical center-side ternary-tree partitioning, and(e) a horizontal center-side ternary-tree partitioning. Tree types otherthan quad-tree and binary-tree have been proposed. In someimplementations, two more ternary tree (TT) partitions, e.g., horizontaland vertical center-side ternary-trees are introduced, as shown in FIG.6 (d) and (e).

In some implementations, there are two levels of trees, region tree(quad-tree) and prediction tree (binary-tree or ternary-tree). A CTU isfirstly partitioned by region tree (RT). A RT leaf may be further splitwith prediction tree (PT). A PT leaf may also be further split with PTuntil max PT depth is reached. A PT leaf is the basic coding unit. It isstill called CU for convenience. A CU cannot be further split.Prediction and transform are both applied on CU in the same way as JEM.The whole partition structure is named ‘multiple-type-tree’.

2.1.5 Example Partitioning Structure

The tree structure referred to as Multi-Tree Type (MTT) is ageneralization of the QTBT. In QTBT, as shown in FIG. 5 , a Coding TreeUnit (CTU) is firstly partitioned by a quad-tree structure. Thequad-tree leaf nodes are further partitioned by a binary-tree structure.

The fundamental structure of MTT constitutes of two types of tree nodes:Region Tree (RT) and Prediction Tree (PT), supporting nine types ofpartitions, as shown in FIG. 7 .

FIG. 7 illustrates examples of (a) a quad-tree partitioning, (b) avertical binary-tree partitioning, (c) a horizontal binary-treepartitioning, (d) a vertical ternary-tree partitioning, (e) a horizontalternary-tree partitioning, (f) a horizontal-up asymmetric binary-treepartitioning, (g) a horizontal-down asymmetric binary-tree partitioning,(h) a vertical-left asymmetric binary-tree partitioning, and (i) avertical-right asymmetric binary-tree partitioning.

A region tree can recursively split a CTU into square blocks down to a4×4 size region tree leaf node. At each node in a region tree, aprediction tree can be formed from one of three tree types: Binary Tree(BT), Ternary Tree (TT), and/or Asymmetric Binary Tree (ABT). In a PTsplit, it may be prohibited to have a quadtree partition in branches ofthe prediction tree. As in JEM, the luma tree and the chroma tree areseparated in I slices. The signaling methods for RT and PT areillustrated in FIG. 8 .

2.2 Inter Prediction in HEVC/H.265

Each inter-predicted PU has motion parameters for one or two referencepicture lists. Motion parameters include a motion vector and a referencepicture index. Usage of one of the two reference picture lists may alsobe signaled using inter_pred_idc. Motion vectors may be explicitly codedas deltas relative to predictors, such a coding mode is called AdvancedMotion Vector Prediction (AMVP) mode.

When a CU is coded with skip mode, one PU is associated with the CU, andthere are no significant residual coefficients, no coded motion vectordelta or reference picture index. A merge mode is specified whereby themotion parameters for the current PU are obtained from neighboring PUs,including spatial and temporal candidates. The merge mode can be appliedto any inter-predicted PU, not only for the skip mode. The alternativeto the merge mode is the explicit transmission of motion parameters,where motion vector, corresponding reference picture index for eachreference picture list, and reference picture list usage are signaledexplicitly per each PU.

When signaling indicates that one of the two reference picture lists isto be used, the PU is produced from one block of samples. This isreferred to as ‘uni-prediction’. Uni-prediction is available both forP-slices and B-slices.

When signaling indicates that both of the reference picture lists are tobe used, the PU is produced from two blocks of samples. This is referredto as ‘bi-prediction’. Bi-prediction is available for B-slices only.

Details on the inter prediction modes are described as follows. Thedescription will begin with the merge mode.

2.2.1 Merge Mode

2.2.1.1 Derivation of Candidates for Merge Mode

When a PU is predicted using the merge mode, an index pointing to anentry in the merge candidates list is parsed from the bitstream and usedto retrieve the motion information. The construction of this list isspecified in the HEVC standard and can be summarized according to thefollowing sequence of steps:

-   -   Step 1: Initial candidates derivation        -   Step 1.1: Spatial candidates derivation        -   Step 1.2: Redundancy check for spatial candidates        -   Step 1.3: Temporal candidates derivation    -   Step 2: Additional candidates insertion        -   Step 2.1: Creation of bi-predictive candidates        -   Step 2.2: Insertion of zero motion candidates

These steps are also schematically depicted in FIG. 9 . For spatialmerge candidate derivation, a maximum of four merge candidates areselected among candidates that are located in five different positions.For temporal merge candidate derivation, a maximum of one mergecandidate is selected among two candidates. Since constant number ofcandidates for each PU is assumed at decoder, additional candidates aregenerated when the number of candidates does not reach to maximum numberof merge candidate (e.g., MaxNumMergeCand) which is signaled in sliceheader. Since the number of candidates is constant, index of best mergecandidate is encoded using truncated unary binarization. If the size ofCU is equal to 8, all the PUs of the current CU share a single mergecandidate list, which is identical to the merge candidate list of the2N×2N prediction unit.

In the following, the operations associated with the aforementionedsteps are detailed.

2.2.1.2 Spatial candidates derivation

In the derivation of spatial merge candidates, a maximum of four mergecandidates are selected among candidates located in the positionsdepicted in FIG. 10 . The order of derivation is A₁, B₁, B₀, A₀ and B₂.Position B₂ is considered only when any PU of position A₁, B₁, B₀, A₀ isnot available (e.g. because it belongs to another slice or tile) or isintra coded. After candidate at position A₁ is added, the addition ofthe remaining candidates is subject to a redundancy check which ensuresthat candidates with same motion information are excluded from the listso that coding efficiency is improved. To reduce computationalcomplexity, not all possible candidate pairs are considered in thementioned redundancy check. Instead only the pairs linked with an arrowin FIG. 11 are considered and a candidate is only added to the list ifthe corresponding candidate used for redundancy check has not the samemotion information. Another source of duplicate motion information isthe “second PU” associated with partitions different from 2N×2N. As anexample, FIG. 12 depicts the second PU for the case of N×2N and 2N×N,respectively. When the current PU is partitioned as N×2N, candidate atposition A₁ is not considered for list construction. In fact, by addingthis candidate will lead to two prediction units having the same motioninformation, which is redundant to just have one PU in a coding unit.Similarly, position B₁ is not considered when the current PU ispartitioned as 2N×N.

2.2.1.3 Temporal Candidate Derivation

In this step, only one candidate is added to the list. Particularly, inthe derivation of this temporal merge candidate, a scaled motion vectoris derived based on co-located PU belonging to the picture which has thesmallest Picture Order Count (POC) difference with current picturewithin the given reference picture list. The reference picture list tobe used for derivation of the co-located PU is explicitly signaled inthe slice header. The scaled motion vector for temporal merge candidateis obtained as illustrated by the dashed line in FIG. 13 , which isscaled from the motion vector of the co-located PU using the POCdistances, tb and td, where tb is defined to be the POC differencebetween the reference picture of the current picture and the currentpicture and td is defined to be the POC difference between the referencepicture of the co-located picture and the co-located picture. Thereference picture index of temporal merge candidate is set equal tozero. For a B-slice, two motion vectors, one is for reference picturelist 0 and the other is for reference picture list 1, are obtained andcombined to make the bi-predictive merge candidate.

In the co-located PU (Y) belonging to the reference frame, the positionfor the temporal candidate is selected between candidates Co and C1, asdepicted in FIG. 14 . If PU at position C₀ is not available, is intracoded, or is outside of the current CTU, position C₁ is used. Otherwise,position C₀ is used in the derivation of the temporal merge candidate.

2.2.1.4 Additional Candidates Insertion

Besides spatio-temporal merge candidates, there are two additional typesof merge candidates: combined bi-predictive merge candidate and zeromerge candidate. Combined bi-predictive merge candidates are generatedby utilizing spatio-temporal merge candidates. Combined bi-predictivemerge candidate is used for B-Slice only. The combined bi-predictivecandidates are generated by combining the first reference picture listmotion parameters of an initial candidate with the second referencepicture list motion parameters of another. If these two tuples providedifferent motion hypotheses, they will form a new bi-predictivecandidate. As an example, FIG. 15 depicts the case when two candidatesin the original list (on the left), which have mvL0 and refIdxL0 or mvL1and refIdxL1, are used to create a combined bi-predictive mergecandidate added to the final list (on the right). There are numerousrules regarding the combinations which are considered to generate theseadditional merge candidates.

Zero motion candidates are inserted to fill the remaining entries in themerge candidates list and therefore hit the MaxNumMergeCand capacity.These candidates have zero spatial displacement and a reference pictureindex which starts from zero and increases every time a new zero motioncandidate is added to the list. The number of reference frames used bythese candidates is one and two for uni and bi-directional prediction,respectively. Finally, no redundancy check is performed on thesecandidates.

2.2.1.5 Motion Estimation Regions for Parallel Processing

To speed up the encoding process, motion estimation can be performed inparallel whereby the motion vectors for all prediction units inside agiven region are derived simultaneously. The derivation of mergecandidates from spatial neighborhood may interfere with parallelprocessing as one prediction unit cannot derive the motion parametersfrom an adjacent PU until its associated motion estimation is completed.To mitigate the trade-off between coding efficiency and processinglatency, HEVC defines the motion estimation region (MER) whose size issignaled in the picture parameter set using the “log2_parallel_merge_level_minus2” syntax element as shown below. When a MERis defined, merge candidates falling in the same region are marked asunavailable and therefore not considered in the list construction.

7.3.2.3 Picture Parameter Set Raw Byte Sequence Payload (RBSP) Syntax

7.3.2.3.1 General Picture Parameter Set RBSP Syntax

Descriptor pic_parameter_set_rbsp( ) { pps_pic_parameter_set_id ue(v)pps_seq_parameter_set_id ue(v) dependent_slice_segments_enabled_flagu(1) ... pps_scaling_list_data_present_flag u(1) if(pps_scaling_list_data_present_flag) scaling_list_data( )lists_modification_present_flag u(1) log2_parallel_merge_level_minus2ue(v) slice_segment_header_extension_present_flag u(1)pps_extension_present_flag u(1) ... rbsp_trailing_bits( ) }log 2_parallel_merge_level_minus2 plus 2 specifies the value of thevariable Log 2ParMrgLevel, which is used in the derivation process forluma motion vectors for merge mode as specified in clause 8.5.3.2.2 andthe derivation process for spatial merging candidates as specified inclause 8.5.3.2.3. The value of log 2_parallel_merge_level_minus2 shallbe in the range of 0 to CtbLog 2SizeY-2, inclusive.

The variable Log 2ParMrgLevel is derived as follows:

Log 2ParMrgLevel=log 2_parallel_merge_level_minus2+2

NOTE 3—The value of Log 2ParMrgLevel indicates the built-in capabilityof parallel derivation of the merging candidate lists. For example, whenLog 2ParMrgLevel is equal to 6, the merging candidate lists for all theprediction units (PUs) and coding units (CUs) contained in a 64×64 blockcan be derived in parallel.

2.2.2 Motion Vector Prediction in AMVP Mode

Motion vector prediction exploits spatio-temporal correlation of motionvector with neighboring PUs, which is used for explicit transmission ofmotion parameters. It constructs a motion vector candidate list byfirstly checking availability of left, above temporally neighboring PUpositions, removing redundant candidates and adding zero vector to makethe candidate list to be constant length. Then, the encoder can selectthe best predictor from the candidate list and transmit thecorresponding index indicating the chosen candidate. Similarly withmerge index signaling, the index of the best motion vector candidate isencoded using truncated unary. The maximum value to be encoded in thiscase is 2 (see FIGS. 2-8 ). In the following sections, details aboutderivation process of motion vector prediction candidate are provided.

2.2.2.1 Derivation of Motion Vector Prediction Candidates

FIG. 16 summarizes derivation process for motion vector predictioncandidate.

In motion vector prediction, two types of motion vector candidates areconsidered: spatial motion vector candidate and temporal motion vectorcandidate. For spatial motion vector candidate derivation, two motionvector candidates are eventually derived based on motion vectors of eachPU located in five different positions as depicted in FIG. 11 .

For temporal motion vector candidate derivation, one motion vectorcandidate is selected from two candidates, which are derived based ontwo different co-located positions. After the first list ofspatio-temporal candidates is made, duplicated motion vector candidatesin the list are removed. If the number of potential candidates is largerthan two, motion vector candidates whose reference picture index withinthe associated reference picture list is larger than 1 are removed fromthe list. If the number of spatio-temporal motion vector candidates issmaller than two, additional zero motion vector candidates is added tothe list.

2.2.2.2 Spatial Motion Vector Candidates

In the derivation of spatial motion vector candidates, a maximum of twocandidates are considered among five potential candidates, which arederived from PUs located in positions as depicted in FIG. 11 , thosepositions being the same as those of motion merge. The order ofderivation for the left side of the current PU is defined as A₀, A₁, andscaled A₀, scaled A₁. The order of derivation for the above side of thecurrent PU is defined as B₀, B₁, B₂, scaled B₀, scaled B₁, scaled B₂.For each side there are therefore four cases that can be used as motionvector candidate, with two cases not required to use spatial scaling,and two cases where spatial scaling is used. The four different casesare summarized as follows.

No Spatial Scaling

-   -   (1) Same reference picture list, and same reference picture        index (same POC)    -   (2) Different reference picture list, but same reference picture        (same POC)    -   Spatial Scaling    -   (3) Same reference picture list, but different reference picture        (different POC)    -   (4) Different reference picture list, and different reference        picture (different POC)

The no-spatial-scaling cases are checked first followed by the spatialscaling. Spatial scaling is considered when the POC is different betweenthe reference picture of the neighbouring PU and that of the current PUregardless of reference picture list. If all PUs of left candidates arenot available or are intra coded, scaling for the above motion vector isallowed to help parallel derivation of left and above MV candidates.Otherwise, spatial scaling is not allowed for the above motion vector.

In a spatial scaling process, the motion vector of the neighboring PU isscaled in a similar manner as for temporal scaling, as depicted as FIG.17 . The main difference is that the reference picture list and index ofcurrent PU is given as input; the actual scaling process is the same asthat of temporal scaling.

2.2.2.3 Temporal Motion Vector Candidates

Apart for the reference picture index derivation, all processes for thederivation of temporal merge candidates are the same as for thederivation of spatial motion vector candidates (see FIGS. 2-6 ). Thereference picture index is signaled to the decoder.

2.2.2.4 Signalling of AMVP Information

For the AMVP mode, four parts may be signalled in the bitstream,including prediction direction, reference index, MVD, and my predictorcandidate index.

Syntax Tables:

Descriptor prediction_unit( x0, y0, nPbW, nPbH ) { if( cu_skip_flag[ x0][ y0 ] ) { if( MaxNumMergeCand > 1 ) merge_idx[ x0 ][ y0 ] ae(v) } else{ /* MODE_INTER */ merge_flag[ x0 ][ y0 ] ae(v) if( merge_flag[ x0 ][ y0] ) { if( MaxNumMergeCand > 1 ) merge_idx[ x0 ][ y0 ] ae(v) } else { if(slice_type == B ) inter_pred_idc[ x0 ][ y0 ] ae(v) if( inter_pred_idc[x0 ][ y0 ] != PRED_L1 ) { if( num_ref_idx_l0_active_minus1 > 0 )ref_idx_l0[ x0 ][ y0 ] ae(v) mvd_coding( x0, y0, 0 ) mvp_l0_flag[ x0 ][y0 ] ae(v) } if( inter_pred_idc[ x0 ][ y0 ] != PRED_L0 ) { if(num_ref_idx_l1_active_minus1 > 0 ) ref_idx_l1[ x0 ][ y0 ] ae(v) if(mvd_l1_zero_flag && inter_pred_idc[ x0 ][ y0 ] == PRED_BI) { MvdL1[ x0][ y0 ][ 0 ] = 0 MvdL1[ x0 ][ y0 ][ 1 ] = 0 } else mvd_coding( x0, y0, 1) mvp_l1_flag[ x0 ][ y0 ] ae(v) } } } }7.3.8.9 Motion Vector Difference Syntax

Descriptor mvd_coding( x0, y0, refList) { abs_mvd_greater0_flag[ 0 ]ae(v) abs_mvd_greater0_flag[ 1 ] ae(v) if( abs_mvd_greater0_flag[ 0 ] )abs_mvd_greater1_flag[ 0 ] ae(v) if( abs_mvd_greater0_flag[ 1 ] )abs_mvd_greater1_flag[ 1 ] ae(v) if( abs_mvd_greater0_flag[ 0 ] ) { if(abs_mvd_greater1_flag[ 0 ] ) abs_mvd_minus2[ 0 ] ae(v) mvd_sign_flag[ 0] ae(v) } if( abs_mvd_greater0_flag[ 1 ] ) { if( abs_mvd_greater1_flag[1 ] ) abs_mvd_minus2[ 1 ] ae(v) mvd_sign_flag[ 1 ] ae(v) } }2.3 New Inter Prediction Methods in Joint Exploration Model (JEM)2.3.1 Sub-CU Based Motion Vector Prediction

In the JEM with QTBT, each CU can have at most one set of motionparameters for each prediction direction. Two sub-CU level motion vectorprediction methods are considered in the encoder by splitting a large CUinto sub-CUs and deriving motion information for all the sub-CUs of thelarge CU. Alternative temporal motion vector prediction (ATMVP) methodallows each CU to fetch multiple sets of motion information frommultiple blocks smaller than the current CU in the collocated referencepicture. In spatial-temporal motion vector prediction (STMVP) methodmotion vectors of the sub-CUs are derived recursively by using thetemporal motion vector predictor and spatial neighbouring motion vector.

To preserve more accurate motion field for sub-CU motion prediction, themotion compression for the reference frames is currently disabled.

2.3.1.1 Alternative Temporal Motion Vector Prediction

In the alternative temporal motion vector prediction (ATMVP) method, themotion vectors temporal motion vector prediction (TMVP) is modified byfetching multiple sets of motion information (including motion vectorsand reference indices) from blocks smaller than the current CU. As shownin FIG. 18 , the sub-CUs are square N×N blocks (N is set to 4 bydefault).

ATMVP predicts the motion vectors of the sub-CUs within a CU in twosteps. The first step is to identify the corresponding block in areference picture with a so-called temporal vector. The referencepicture is called the motion source picture. The second step is to splitthe current CU into sub-CUs and obtain the motion vectors as well as thereference indices of each sub-CU from the block corresponding to eachsub-CU, as shown in FIG. 18 .

In the first step, a reference picture and the corresponding block isdetermined by the motion information of the spatial neighbouring blocksof the current CU. To avoid the repetitive scanning process ofneighbouring blocks, the first merge candidate in the merge candidatelist of the current CU is used. The first available motion vector aswell as its associated reference index are set to be the temporal vectorand the index to the motion source picture. This way, in ATMVP, thecorresponding block may be more accurately identified, compared withTMVP, wherein the corresponding block (sometimes called collocatedblock) is always in a bottom-right or center position relative to thecurrent CU. In one example, if the first merge candidate is from theleft neighboring block (e.g., Ai in FIG. 19 ), the associated MV andreference picture are utilized to identify the source block and sourcepicture.

In the second step, a corresponding block of the sub-CU is identified bythe temporal vector in the motion source picture, by adding to thecoordinate of the current CU the temporal vector. For each sub-CU, themotion information of its corresponding block (the smallest motion gridthat covers the center sample) is used to derive the motion informationfor the sub-CU. After the motion information of a corresponding N×Nblock is identified, it is converted to the motion vectors and referenceindices of the current sub-CU, in the same way as TMVP of HEVC, whereinmotion scaling and other procedures apply. For example, the decoderchecks whether the low-delay condition (e.g., the POCs of all referencepictures of the current picture are smaller than the POC of the currentpicture) is fulfilled and possibly uses motion vector MV_(x) (the motionvector corresponding to reference picture list X) to predict motionvector MV_(y) (with X being equal to 0 or 1 and Y being equal to 1−X)for each sub-CU.

2.3.1.2 Spatial-Temporal Motion Vector Prediction

In this method, the motion vectors of the sub-CUs are derivedrecursively, following raster scan order. FIG. 20 illustrates an exampleof one CU with four sub-blocks (A-D) and its neighbouring blocks (a-d).Consider an 8×8 CU which contains four 4×4 sub-CUs A, B, C, and D. Theneighbouring 4×4 blocks in the current frame are labelled as a, b, c,and d.

The motion derivation for sub-CU A starts by identifying its two spatialneighbours. The first neighbour is the N×N block above sub-CU A (blockc). If this block c is not available or is intra coded the other N×Nblocks above sub-CU A are checked (from left to right, starting at blockc). The second neighbour is a block to the left of the sub-CU A (blockb). If block b is not available or is intra coded other blocks to theleft of sub-CU A are checked (from top to bottom, staring at block b).The motion information obtained from the neighbouring blocks for eachlist is scaled to the first reference frame for a given list. Next,temporal motion vector predictor (TMVP) of sub-block A is derived byfollowing the same procedure of TMVP derivation as specified in HEVC.The motion information of the collocated block at location D is fetchedand scaled accordingly. Finally, after retrieving and scaling the motioninformation, all available motion vectors (up to 3) are averagedseparately for each reference list. The averaged motion vector isassigned as the motion vector of the current sub-CU.

2.3.1.3 Sub-CU Motion Prediction Mode Signalling

The sub-CU modes are enabled as additional merge candidates and there isno additional syntax element required to signal the modes. Twoadditional merge candidates are added to merge candidates list of eachCU to represent the ATMVP mode and STMVP mode. Up to seven mergecandidates are used, if the sequence parameter set indicates that ATMVPand STMVP are enabled. The encoding logic of the additional mergecandidates is the same as for the merge candidates in the HM, whichmeans, for each CU in P or B slice, two more RD checks is needed for thetwo additional merge candidates.

In the JEM, all bins of merge index are context coded by CABAC. While inHEVC, only the first bin is context coded and the remaining bins arecontext by-pass coded.

2.3.2 Adaptive Motion Vector Difference Resolution

In HEVC, motion vector differences (MVDs) (between the motion vector andpredicted motion vector of a PU) are signalled in units of quarter lumasamples when use_integer_mv_flag is equal to 0 in the slice header. Inthe JEM, a locally adaptive motion vector resolution (LAMVR) isintroduced. In the JEM, MVD can be coded in units of quarter lumasamples, integer luma samples or four luma samples. The MVD resolutionis controlled at the coding unit (CU) level, and MVD resolution flagsare conditionally signalled for each CU that has at least one non-zeroMVD components.

For a CU that has at least one non-zero MVD components, a first flag issignalled to indicate whether quarter luma sample MV precision is usedin the CU. When the first flag (equal to 1) indicates that quarter lumasample MV precision is not used, another flag is signalled to indicatewhether integer luma sample MV precision or four luma sample MVprecision is used.

When the first MVD resolution flag of a CU is zero, or not coded for aCU (meaning all MVDs in the CU are zero), the quarter luma sample MVresolution is used for the CU. When a CU uses integer-luma sample MVprecision or four-luma-sample MV precision, the MVPs in the AMVPcandidate list for the CU are rounded to the corresponding precision.

In the encoder, CU-level RD checks are used to determine which MVDresolution is to be used for a CU. That is, the CU-level RD check isperformed three times for each MVD resolution. To accelerate encoderspeed, the following encoding schemes are applied in the JEM.

During RD check of a CU with normal quarter luma sample MVD resolution,the motion information of the current CU (integer luma sample accuracy)is stored. The stored motion information (after rounding) is used as thestarting point for further small range motion vector refinement duringthe RD check for the same CU with integer luma sample and 4 luma sampleMVD resolution so that the time-consuming motion estimation process isnot duplicated three times.

RD check of a CU with 4 luma sample MVD resolution is conditionallyinvoked. For a CU, when RD cost integer luma sample MVD resolution ismuch larger than that of quarter luma sample MVD resolution, the RDcheck of 4 luma sample MVD resolution for the CU is skipped.

2.3.3 Pattern Matched Motion Vector Derivation

Pattern matched motion vector derivation (PMMVD) mode is a special mergemode based on Frame-Rate Up Conversion (FRUC) techniques. With thismode, motion information of a block is not signalled but derived atdecoder side.

A FRUC flag is signalled for a CU when its merge flag is true. When theFRUC flag is false, a merge index is signalled and the regular mergemode is used. When the FRUC flag is true, an additional FRUC mode flagis signalled to indicate which method (bilateral matching or templatematching) is to be used to derive motion information for the block.

At encoder side, the decision on whether using FRUC merge mode for a CUis based on RD cost selection as done for normal merge candidate. Thatis the two matching modes (bilateral matching and template matching) areboth checked for a CU by using RD cost selection. The one leading to theminimal cost is further compared to other CU modes. If a FRUC matchingmode is the most efficient one, FRUC flag is set to true for the CU andthe related matching mode is used.

Motion derivation process in FRUC merge mode has two steps. A CU-levelmotion search is first performed, then followed by a Sub-CU level motionrefinement. At CU level, an initial motion vector is derived for thewhole CU based on bilateral matching or template matching. First, a listof MV candidates is generated and the candidate which leads to theminimum matching cost is selected as the starting point for further CUlevel refinement. Then a local search based on bilateral matching ortemplate matching around the starting point is performed and the MVresults in the minimum matching cost is taken as the MV for the whole

CU. Subsequently, the motion information is further refined at sub-CUlevel with the derived CU motion vectors as the starting points.

For example, the following derivation process is performed for a W×H CUmotion information derivation. At the first stage, MV for the whole W×HCU is derived. At the second stage, the CU is further split into M×Msub-CUs. The value of M is calculated as in Eq. (1), D is a predefinedsplitting depth which is set to 3 by default in the JEM. Then the MV foreach sub-CU is derived.

$\begin{matrix}{M = {\max\left\{ {4,{\min\left\{ {\frac{M}{2^{D}},\frac{N}{2^{D}}} \right\}}} \right\}}} & {{Eq}.\mspace{14mu}(1)}\end{matrix}$

As shown in the FIG. 21 , the bilateral matching is used to derivemotion information of the current CU by finding the closest matchbetween two blocks along the motion trajectory of the current CU in twodifferent reference pictures. Under the assumption of continuous motiontrajectory, the motion vectors MV0 and MV1 pointing to the two referenceblocks shall be proportional to the temporal distances, e.g., TD0 andTD1, between the current picture and the two reference pictures. As aspecial case, when the current picture is temporally between the tworeference pictures and the temporal distance from the current picture tothe two reference pictures is the same, the bilateral matching becomesmirror based bi-directional MV.

As shown in FIG. 22 , template matching is used to derive motioninformation of the current CU by finding the closest match between atemplate (top and/or left neighbouring blocks of the current CU) in thecurrent picture and a block (same size to the template) in a referencepicture. Except the aforementioned FRUC merge mode, the templatematching is also applied to AMVP mode. In the JEM, as done in HEVC, AMVPhas two candidates. With template matching method, a new candidate isderived. If the newly derived candidate by template matching isdifferent to the first existing AMVP candidate, it is inserted at thevery beginning of the AMVP candidate list and then the list size is setto two (meaning remove the second existing AMVP candidate). When appliedto AMVP mode, only CU level search is applied.

2.3.3.1 CU Level MV Candidate Set

The MV Candidate Set at CU Level Includes:

-   -   (i) Original AMVP candidates if the current CU is in AMVP mode    -   (ii) all merge candidates,    -   (iii) several MVs in the interpolated MV field, which is        introduced in section [00175].    -   (iv) top and left neighbouring motion vectors

When using bilateral matching, each valid MV of a merge candidate isused as an input to generate a MV pair with the assumption of bilateralmatching. For example, one valid MV of a merge candidate is (MVa, refa)at reference list A. Then the reference picture refb of its pairedbilateral MV is found in the other reference list B so that refa andrefb are temporally at different sides of the current picture. If such arefb is not available in reference list B, refb is determined as areference which is different from refa and its temporal distance to thecurrent picture is the minimal one in list B. After refb is determined,MVb is derived by scaling MVa based on the temporal distance between thecurrent picture and refa, refb.

Four MVs from the interpolated MV field are also added to the CU levelcandidate list. More specifically, the interpolated MVs at the position(0, 0), (W/2, 0), (0, H/2) and (W/2, H/2) of the current CU are added.

When FRUC is applied in AMVP mode, the original AMVP candidates are alsoadded to CU level MV candidate set.

At the CU level, up to 15 MVs for AMVP CUs and up to 13 MVs for mergeCUs are added to the candidate list.

2.3.3.2 Sub-CU Level MV Candidate Set

The MV Candidate Set at Sub-CU Level Includes:

-   -   (i) an MV determined from a CU-level search,    -   (ii) top, left, top-left and top-right neighbouring MVs,    -   (iii) scaled versions of collocated MVs from reference pictures,    -   (iv) up to 4 ATMVP candidates,    -   (v) up to 4 STMVP candidates

The scaled MVs from reference pictures are derived as follows. All thereference pictures in both lists are traversed. The MVs at a collocatedposition of the sub-CU in a reference picture are scaled to thereference of the starting CU-level MV.

ATMVP and STMVP candidates are limited to the four first ones. At thesub-CU level, up to 17 MVs are added to the candidate list.

2.3.3.3 Generation of Interpolated MV Field

Before coding a frame, interpolated motion field is generated for thewhole picture based on unilateral ME. Then the motion field may be usedlater as CU level or sub-CU level

MV candidates.

First, the motion field of each reference pictures in both referencelists is traversed at 4×4 block level. For each 4×4 block, if the motionassociated to the block passing through a 4×4 block in the currentpicture (as shown in FIG. 23 ) and the block has not been assigned anyinterpolated motion, the motion of the reference block is scaled to thecurrent picture according to the temporal distance TD0 and TD1 (the sameway as that of MV scaling of TMVP in HEVC) and the scaled motion isassigned to the block in the current frame. If no scaled MV is assignedto a 4×4 block, the block's motion is marked as unavailable in theinterpolated motion field.

2.3.3.4 Interpolation and Matching Cost

When a motion vector points to a fractional sample position, motioncompensated interpolation is needed. To reduce complexity, bi-linearinterpolation instead of regular 8-tap HEVC interpolation is used forboth bilateral matching and template matching.

The calculation of matching cost is a bit different at different steps.When selecting the candidate from the candidate set at the CU level, thematching cost is the absolute sum difference (SAD) of bilateral matchingor template matching. After the starting MV is determined, the matchingcost C of bilateral matching at sub-CU level search is calculated asfollows:C=SAD+w·(|MV _(x) −MV _(x) ² |+|MV _(y) −MV _(y) ²|)  Eq. (2)

where w is a weighting factor which is empirically set to 4, MV andMV^(s) indicate the current MV and the starting MV, respectively. SAD isstill used as the matching cost of template matching at sub-CU levelsearch.

In FRUC mode, MV is derived by using luma samples only. The derivedmotion will be used for both luma and chroma for MC inter prediction.After MV is decided, final MC is performed using 8-taps interpolationfilter for luma and 4-taps interpolation filter for chroma.

2.3.3.5 MV Refinement

MV refinement is a pattern based MV search with the criterion ofbilateral matching cost or template matching cost. In the JEM, twosearch patterns are supported—an unrestricted center-biased diamondsearch (UCBDS) and an adaptive cross search for MV refinement at the CUlevel and sub-CU level, respectively. For both CU and sub-CU level MVrefinement, the MV is directly searched at quarter luma sample MVaccuracy, and this is followed by one-eighth luma sample MV refinement.The search range of MV refinement for the CU and sub-CU step are setequal to 8 luma samples.

2.3.3.6 Selection of Prediction Direction in Template Matching FRUCMerge Mode

In the bilateral matching merge mode, bi-prediction is always appliedsince the motion information of a CU is derived based on the closestmatch between two blocks along the motion trajectory of the current CUin two different reference pictures. There is no such limitation for thetemplate matching merge mode. In the template matching merge mode, theencoder can choose among uni-prediction from list0, uni-prediction fromlist1 or bi-prediction for a CU. The selection is based on a templatematching cost as follows:

If costBi <= factor * min (cost0, cost1) bi-prediction is used;Otherwise, if cost0 <= cost1 uni-prediction from list0 is used;Otherwise, uni-prediction from list1 is used;

where cost0 is the SAD of list0 template matching, cost1 is the SAD oflist1 template matching and costBi is the SAD of bi-prediction templatematching. The value of factor is equal to 1.25, which means that theselection process is biased toward bi-prediction. The inter predictiondirection selection is only applied to the CU-level template matchingprocess.

2.3.4 Decoder-Side Motion Vector Refinement

In bi-prediction operation, for the prediction of one block region, twoprediction blocks, formed using a motion vector (MV) of list0 and a MVof list1, respectively, are combined to form a single prediction signal.In the decoder-side motion vector refinement (DMVR) method, the twomotion vectors of the bi-prediction are further refined by a bilateraltemplate matching process. The bilateral template matching applied inthe decoder to perform a distortion-based search between a bilateraltemplate and the reconstruction samples in the reference pictures inorder to obtain a refined MV without transmission of additional motioninformation.

In DMVR, a bilateral template is generated as the weighted combination(i.e. average) of the two prediction blocks, from the initial MV0 oflist0 and MV1 of list1, respectively, as shown in FIG. 23 . The templatematching operation consists of calculating cost measures between thegenerated template and the sample region (around the initial predictionblock) in the reference picture. For each of the two reference pictures,the MV that yields the minimum template cost is considered as theupdated MV of that list to replace the original one. In the JEM, nine MVcandidates are searched for each list. The nine MV candidates includethe original MV and 8 surrounding MVs with one luma sample offset to theoriginal MV in either the horizontal or vertical direction, or both.Finally, the two new MVs, i.e., MV0′ and MV1′ as shown in FIG. 24 , areused for generating the final bi-prediction results. A sum of absolutedifferences (SAD) is used as the cost measure.

DMVR is applied for the merge mode of bi-prediction with one MV from areference picture in the past and another from a reference picture inthe future, without the transmission of additional syntax elements. Inthe JEM, when LIC, affine motion, FRUC, or sub-CU merge candidate isenabled for a CU, DMVR is not applied.

3. Example Problems and Embodiments

Several problems have been identified with regard the current codingtechniques.

First, for different partition trees like BT or TT, a parent node mayhave two or three child nodes, such as one block is split to two orthree sub-blocks. In current design, the two or three child nodes mayshare the same motion information. In this case, unnecessary overheadsto signal the motion information may be required. Instead of codingmultiple child nodes, a smart encoder can code the block as a wholewithout further splitting to reduce signaling overhead. Alternatively,child nodes may have different motion information to avoid redundantsignaling in the bitstream.

Second, the MER was designed to cover a N×N region, mainly forconsidering the square CU or CTU design in HEVC. However, in VVC,non-square CU or even non-square CTU may appear. There is a need for theMER to be adaptive to non-square CU/CTU.

Third, currently, only one TMVP candidate can be added to the mergecandidate list.

Adding more temporal merge candidates are expected to provide additionalcoding gains.

Lastly, combined bi-prediction merge candidate is only one way togenerate some virtual merge candidate (e.g., not directly copied/scaledfrom spatial/temporal neighbouring blocks). It is desirable to developdifferent ways to generate virtual merge candidates, which may bringadditional benefits.

The example embodiments below illustrate various techniques that can beimplemented to address the problems mentioned above.

Examples Related to MER

Example A1

MER region size may depend on the partition type (e.g., QT, BT or TT)and/or block shape (square or non-square) and/or block sizes and/ortemporal layer index of the current picture.

-   -   a. In some embodiments, MER region sizes may be signaled in the        bitstream, e.g., in sequence parameter set (SPS), picture        parameter set (PPS), slice header etc.

Example A2

A non-square MER region of M×N (M is unequal to N) can be introduced toallow the encoder/decoder to do parallel coding.

-   -   a. In one example, two separate syntax elements to indicate the        width and height of the MER region may be transmitted in the        bitstream, e.g., sequence parameter set (SPS), picture parameter        set (PPS), slice header etc.    -   b. In another example, for each partition type (e.g., QT, BT,        ABT or TT) and/or block shape (square or non-square), separate        indications of width and height of the MER region may be        transmitted in the bitstream, e.g., sequence parameter set        (SPS), picture parameter set (PPS), slice header etc.    -   c. In some embodiments, prediction coding of two syntax elements        may be applied to save some overhead for indications of        width/height of the MER region.    -   d. In some embodiments, one flag may be signaled to indicate        whether the two/multiple syntax elements share the same sizes.        Examples Related to Restriction of Motion Information Due to        Partitions

Example B1

For one partition type (e.g., QT, BT, ABT or TT), one block may be splitto M sub-blocks (M>=2). A restriction may be imposed such that not allof the M sub-blocks share the same motion information, which includesreference pictures, motion vectors, IC flags, affine flags, and so on.

-   -   a. If the first N (e.g., N=M−1) sub-blocks are coded with the        same motion information, the remaining sub-block(s) (e.g., the        last sub-block) do not have the same motion information.    -   b. In one example, the signaling of motion information of the        remaining sub-block(s) (e.g., the last sub-block) in the coding        order is avoided if they use the same motion information.        -   i. When the first subset of sub-blocks (e.g., the first M−1            sub-blocks) is coded with the same motion information, if            the remaining subset of sub-blocks (e.g., the last            sub-block) is coded with the merge mode, the merge index            does not correspond to the motion information of a spatial            neighboring block covered by any of the first subset of            sub-blocks (e.g., the M−1 sub-blocks). In other words, a            merge index that corresponds to the motion information of a            spatial neighboring block covered by any of the first subset            of sub-blocks (e.g., the M−1 sub-blocks) is not signaled in            the bitstream (e.g., for bitstream conformance reasons).        -   ii. When the first subset of sub-blocks (e.g., the first M−1            sub-blocks) is coded with the same motion information, if            the remaining subset of sub-blocks (e.g., the last            sub-block) is coded with the merge mode, the merge candidate            providing the same motion information of the first subset of            sub-blocks (e.g., the previous M−1 sub-blocks) is removed            from the merge candidate list.        -   iii. When the first subset of sub-blocks (e.g., the first            M−1 sub-blocks) is coded with the same motion information,            if the remaining subset of sub-blocks (e.g., the last            sub-block) is coded with the AMVP mode and the coded            reference pictures are the same as those for the first            subset of sub-blocks (e.g., the M−1 sub-blocks), the decoded            AMVP MV predictor candidate index does not correspond to the            motion information of a spatial neighboring block covered by            any of the first subset of sub-blocks (e.g., M−1            sub-blocks). In other words, if any one of the MV predictor            candidate index could result in the same motion information,            the signaling is modified to skip the indication of this MV            predictor candidate. Alternatively, furthermore, if there            are only two AMVP candidates, the signaling of MV predictor            candidate index can be skipped.        -   iv. When the first subset of sub-blocks (e.g., the first M−1            sub-blocks) is coded with the same motion information, if            the remaining subset of sub-blocks (e.g., the last            sub-block) is coded with the DMVR mode, the cost calculation            of the refined motion information which are identical to            those for the first subset of sub-blocks (e.g., the M−1            sub-blocks) is skipped and the cost value is considered to a            maximum value.        -   v. When the first subset of sub-blocks (e.g., the first M−1            sub-blocks) is coded with the same motion information, if            the remaining subset of sub-blocks (e.g., the last            sub-block) is coded with the FRUC mode, the cost calculation            of the motion information which are identical to those for            the first subset (e.g., the M−1 sub-blocks) is skipped and            the cost value is considered to a maximum value.

Example B2

Restrictions can be imposed such that merge candidates may not beobtained from a neighboring block which can form a parent node togetherwith the current block.

As discussed above, a maximum of four merge candidates are selectedamong candidates located in the positions depicted in FIG. 10 . A subsetof these positions that are located within the parent node can be markedas restricted or disallowed so that the merge candidates are determinedbased on neighboring blocks outside of the parent node.

-   -   a. In one example, when deriving the merge candidate list for        the BT or ABT case, the second partition (e.g., the second child        node) of a parent node does not utilize any neighboring block        located in the first BT or ABT partition (e.g., first child        node). FIGS. 26A-26B show some examples. FIG. 26A shows examples        of a 2^(nd) CU of a parent node under ABT partition structures        in accordance with one or more embodiments of the disclosed        technology. In the left section of FIG. 26A, a parent node 2601        is split into two CUs using an ABT partition structure. A        neighboring block 2603 in the first CU is considered to be in a        disallowed position. Thus, the merge candidates are derived        solely based on the neighboring blocks of the parent node 2611        regardless of how the CUSs are partitioned—that is, the        neighboring blocks located outside of the parent node. In the        right section of FIG. 26A, a parent node 2611 is split into two        CUs using another ABT partition structure. A neighboring block        2613 in the first CU is disallowed, thus the merge candidates        are derived solely based on the neighboring blocks of the parent        node 2611. FIG. 26B shows examples of CUs under TT partition        structures in accordance with one or more embodiments of the        disclosed technology. In the left section of FIG. 26B, a        neighboring block of 3^(rd) CU (in the 2^(nd) CU) is considered        to be in a disallowed position. The merge candidates are derived        solely based on the neighboring blocks of the parent node        regardless of the TT partition structure. Similarly, in the        right section of FIG. 26B, a neighboring block of the 2^(nd) CU        (positioned in the 1^(st) CU) is considered to be in a        disallowed position. Thus, the merge candidates are derived        based on solely the neighboring blocks of the parent node        regardless of the partition structure. Similar restrictions can        be applied to other partition structures (e.g., QT) as well.    -   b. In one example, when deriving the merge candidate list for        the TT case, the second or the third partition (e.g., the second        or the third child node) does not utilize any neighboring block        located in the first TT partition and/or the second TT        partition.    -   c. Alternatively, furthermore, if there are some neighboring        blocks at the disallowed positions, additional neighboring        blocks may be further accessed to derive merge candidates.        -   i. In one example, a new position is accessed and treated as            the replacement of the disallowed position. In this case,            the derived merge candidate from the new position is used as            a replacement of the merge candidate derived from the            disallowed positions.        -   ii. Alternatively, all the allowed positions are firstly            checked in order, followed by new positions. In this case,            the derived merge candidates from new positions may only be            added after all the merge candidates derived from allowed            positions.        -   iii. Alternatively, certain order may be defined to add            merge candidates from allowed and new positions. In this            case, for different CUs, different order may be utilized to            add merge candidates derived from different positions.

Example B3

The above restrictions in Example B1 and B2 can also be applicable tothe AMVP candidate derivation process.

Examples Related to Merge Candidates

Example C1

Virtual merge candidate(s) derived by modifying a motion vector and/or areference picture of an available merge candidate can be added to themerge candidate list. For example, virtual merge candidates can bederived by scaling motion vectors of one available merge candidate todifferent reference pictures.

-   -   a. In one example, prediction direction is inherited from the        available merge candidate, and motion vector and reference        picture index are modified.        -   i. For each available reference picture list (prediction            direction from L0 or L1), the associated motion vector may            be scaled to a different reference picture in the same            reference picture list, or the other reference picture list.        -   ii. If the available merge candidate corresponds to            bi-prediction, one virtual merge candidate may be derived by            modifying the motion information of only one reference            picture list. In one example, for one reference picture            list, the associated reference picture (or reference picture            index) and motion vector is inherited by the virtual merge            candidate, while for the other reference picture list, the            associated reference picture (or reference picture index)            and motion vector may be modified by scaling the motion            vector to a different reference picture in the same            reference picture list.    -   b. In one example, if the available merge candidate corresponds        to uni-prediction, the prediction direction of the virtual merge        candidate may be modified to be bi-prediction.        -   i. For the available reference picture list (uni-prediction            corresponding to, e.g., List X), the associated reference            picture (or reference picture index) and motion vector is            inherited by the virtual merge candidate, while for List            (1−X), the motion vector may be derived by scaling the            motion vector from List X to a reference picture in the            other reference picture list (List (1−X)) and the reference            picture (or reference picture index) is set to the reference            picture in List (1−X) where the motion vector is scaled to.            -   1. When the reference picture in List (1−X) is same with                the reference picture in List X, motion vector in List                (1−X) is derived by adding an arbitrary offset to the                motion vector in List X. For example, offset (−1, 0),                (0, −1), (1, 0), (0, 1) etc. al, may be added to the                motion vector.    -   c. Multiple virtual merge candidates may be derived by selecting        one available merge candidate, but scaled to multiple reference        pictures.    -   d. Multiple virtual merge candidates may be derived by selecting        multiple available merge candidates but for one selected        available merge candidate, only one virtual merge candidate may        be derived.        -   i. Alternatively, for one selected available merge            candidate, M (M>1) virtual merge candidate may be derived.    -   e. The selection of one or more available merge candidates may        depend on:        -   i. Based on the inserted order of the available merge            candidates. In one example, only the first N candidates may            be used to derive the virtual merge candidates        -   ii. Based on whether one available merge candidate            corresponds to bi-prediction        -   iii. Based on the type of the merge candidates (spatial            merge candidates, temporal merge candidates, combined            bi-prediction merge candidates, zero motion vector merge            candidates, sub-block merge candidates). In one example,            only spatial merge candidates may be used to derive virtual            merge candidates.        -   iv. Based on the coded modes of the merge candidates (affine            or non-affine motion, illumination compensation (IC) enabled            or disabled). In one example, only non-affine and non-IC            merge candidates may be used to derive virtual merge            candidates.        -   v. Based on the size and shape of the current block.        -   vi. Based on the coding modes of neighboring blocks.    -   f. The selection of one or more reference pictures where motion        vectors are to be scaled to may depend on:        -   i. reference picture index. In one example, reference            pictures with smaller reference indices are selected, e.g.            reference picture index equal to 0.        -   ii. The picture order count (POC) difference between one            reference picture and the reference picture associated with            the selected available merge candidate. In one example, a            reference picture for each reference picture list with            smallest POC difference is chosen.        -   iii. The quantization parameter (QP) difference between one            reference picture and the reference picture associated with            the selected available merge candidate. In one example, a            reference picture for each reference picture list with            smallest QP difference is chosen.        -   iv. The temporal layers of reference pictures. In one            example, a reference picture with the lowest temporal layer            is chosen.    -   g. Virtual merge candidates may be added to the merge candidate        list at certain positions, such as before TMVP, or after TMVP        but before combined bi-predictive merge candidates, or after        combined bi-predictive merge candidates.        -   i. When multiple virtual merge candidates may be added,            those Bi-prediction based merge candidates have a higher            priority compared to uni-prediction based merge candidates,            i.e., bi-prediction candidates are added before            uni-prediction candidates.        -   ii. When multiple reference pictures may be used to scale            motion vectors associated with a selected merge candidate,            the order of reference pictures may be as follows:            -   1. Based on the increasing order of reference picture                index.            -   2. Pictures in List 0 are checked before pictures in                List 1 or vice versa.            -   3. Pictures in List 0 and List 1 are checked interleaved                according to the reference picture index.            -   4. In one example, for bi-prediction, keep the list 1                motion information unchanged, but loop all the reference                pictures in List 0 according to increasing order of                reference picture index; then keep the list 0 motion                information, but loop all the reference pictures in List                1 according to increasing order of reference picture                index. Alternatively, keep the list 0 motion information                unchanged, but loop all the reference pictures in List 1                according to increasing order of reference picture                index; then keep the list 1 motion information, but loop                all the reference pictures in List 0 according to                increasing order of reference picture index.                Alternatively, scale motion information to the two                reference pictures with index equal to 0, then scale to                two reference pictures with index equal to 1, and so on.    -   h. Virtual merge candidates may have more than two reference        blocks, i.e. multiple hypothesis with more than two references.

Example C2

Sub-block motion candidates may be obtained from a block identified bymotion vector(s) of a spatial merge candidate and the relative positionsbetween the current block and the block wherein spatial merge candidateis from.

-   -   a. An illustrative example is depicted in FIG. 25 which shows        illustrative examples of source block identification.    -   b. The concept of adding the relative position between a spatial        neighboring block and the current block may be also applied to        sub-block motion candidates for intra block copy (IBC) merge        within current frame or affine merge. In this case, the source        picture will be the same as the current picture. The concept can        also be applied for ATMVP in a different picture from the        current picture of the current block.

Example C3

During the TMVP derivation process, the co-located block may beidentified by a non-zero motion vector instead of choosing theco-located position (zero motion vector).

-   -   a. The non-zero motion vector may be derived from a spatial        merge candidate.    -   b. In one example, the same way as used in ATMVP may be        utilized, such as the first merge candidate by scaling the        motion vector to the co-located picture, if necessary.    -   c. Alternatively, the co-located picture may be also modified,        such as set to the reference picture associated with one spatial        merge candidate.

Example C4

Multiple blocks from one or multiple col-pictures may be used to derivemultiple TMVP candidates.

-   -   a. In one example, the multiple blocks may be located within the        co-located block wherein the co-located block is the block with        the same relative position to the top-left of the co-located        picture as the current block, and with the same size as the        current block.    -   b. In one example, the multiple blocks may be located within the        co-located CTB wherein the co-located CTB is the CTB covering        the co-located block.    -   c. In one example, the multiple blocks may be located outside        the co-located block, and/or co-located CTB.    -   d. Alternatively, furthermore, in above examples, the co-located        block may be defined in different ways, i.e., pointed by a        motion vector derived from some merge candidate or derived from        motion information of spatial neighboring block(s). FIG. 26C        shows an example of multiple blocks for TMVP candidate        derivation outside the col-located block (some may be also        outside the co-located). FIG. 26D shows an example of multiple        blocks for TMVP candidate derivation within the col-located        Coding Tree Unit (CTU). FIG. 26E shows an example of multiple        blocks for TMVP candidate derivation outside the col-located        block (some may also be outside the co-located.

Example C5

For those newly introduced candidates, full pruning or partial pruningmay be applied.

-   -   a. For full pruning, one new candidate should be checked with        all the other available candidates (inserted before the new        candidate) to see whether any two of them are identical. If the        new candidate is identical to any one, the new candidate is not        added to the candidate list.    -   b. For partial pruning, one new candidate should be checked with        partial of other available candidates (inserted before the new        candidate) to see whether any two of them are identical.

Another embodiment is given as follows. This specific embodimentillustrates changes that can be made to the currently defined HEVCcoding standard to accommodate some implementations of the disclosedtechnology. The section numbers below refer to the corresponding sectionnumbers in the HEVC standard document. In the text, underlined textrepresents addition and strikethrough indicates deletion to the currentstandard. Furthermore, the designation “X” and “Y” are added to variablenames to indicate the two new bit fields defined for the bitstream.

7.3.2.3 Picture Parameter Set RBSP Syntax

7.3.2.3.1 General Picture Parameter Set RBSP Syntax

Descriptor pic_parameter_set_rbsp( ) { pps_pic_parameter_set_id ue(v)pps_seq_parameter_set_id ue(v) dependent_slice_segments_enabled_flagu(1) ... pps_scaling_list_data_present_flag u(1) if(pps_scaling_list_data_present_flag) scaling_list_data( )lists_modification_present_flag u(1)

log2X_parallel_merge_level_minus2 ue(v)log2Y_parallel_merge_level_minus2 ue(v)slice_segment_header_extension_present_flag u(1)pps_extension_present_flag u(1) ... rbsp_trailing_bits( ) }log 2X_parallel_merge_level_minus2 plus 2 specifies the value of thevariable Log 2XParMrgLevel, which is used in the derivation process forluma motion vectors for merge mode as specified in clause 8.5.3.2.2 andthe derivation process for spatial merging candidates as specified inclause 8.5.3.2.3. The value of log 2X_parallel_merge_level_minus2 shallbe in the range of 0 to CtbLog 2SizeY−2, inclusive.

The variable Log 2ParMrgLevel is derived as follows:Log 2XParMrgLevel=log 2X_parallel_merge_level_minus2+2  (7-37)log 2Y_parallel_merge_level_minus2 plus 2 specifies the value of thevariable Log 2YParMrgLevel, which is used in the derivation process forluma motion vectors for merge mode as specified in clause 8.5.3.2.2 andthe derivation process for spatial merging candidates as specified inclause 8.5.3.2.3. The value of log 2Y_parallel_merge_level_minus2 shallbe in the range of 0 to CtbLog 2SizeY−2, inclusive.

The variable Log 2YParMrgLevel is derived as follows:Log 2YParMrgLevel=log 2Y_parallel_merge_level_minus2+2  (7-37)Derivation Process for Spatial Merging Candidates

Inputs to this process are:

-   -   a luma location (xCb, yCb) of the top-left sample of the current        luma coding block relative to the top-left luma sample of the        current picture,    -   a variable nCbS specifying the size of the current luma coding        block,    -   a luma location (xPb, yPb) specifying the top-left sample of the        current luma prediction block relative to the top-left luma        sample of the current picture,    -   two variables nPbW and nPbH specifying the width and the height        of the luma prediction block,    -   a variable partIdx specifying the index of the current        prediction unit within the current coding unit.

Outputs of this process are as follows, with X being 0 or 1:

-   -   the availability flags availableFlagA₀, availableFlagA₁,        availableFlagB₀, availableFlagB₁, and availableFlagB₂ of the        neighbouring prediction units,    -   the reference indices refIdxLXA₀, refIdxLXA₁, refIdxLXB₀,        refIdxLXB₁, and refIdxLXB₂ of the neighbouring prediction units,    -   the prediction list utilization flags predFlagLXA₀,        predFlagLXA₁, predFlagLXB₀, predFlagLXB₁, and predFlagLXB₂ of        the neighbouring prediction units,    -   the motion vectors mvLXA₀, mvLXA₁, mvLXB₀, mvLXB₁, and mvLXB₂ of        the neighbouring prediction units.

For the derivation of availableFlagA₁, refIdxLXA₁, predFlagLXA₁, andmvLXA₁ the following applies:

-   -   The luma location (xNbA₁, yNbA₁) inside the neighbouring luma        coding block is set equal to (xPb−1, yPb+nPbH−1).    -   The availability derivation process for a prediction block as        specified in clause 6.4.2 is invoked with the luma location        (xCb, yCb), the current luma coding block size nCbS, the luma        prediction block location (xPb, yPb), the luma prediction block        width nPbW, the luma prediction block height nPbH, the luma        location (xNbA₁, yNbA₁), and the partition index partIdx as        inputs, and the output is assigned to the prediction block        availability flag availableA₁.    -   When one or more of the following conditions are true,        availableA₁ is set equal to FALSE:    -   xPb>>Log 2XParMrgLevel is equal to xNbA₁>>Log 2XParMrgLevel and        yPb>>Log 2YParMrgLevel is equal to yNbA₁>>Log 2YParMrgLevel.    -   PartMode of the current prediction unit is equal to PART_Nx2N,        PART_nLx2N, or PART_nRx2N, and partIdx is equal to 1.    -   The variables availableFlagA₁, refIdxLXA₁, predFlagLXA₁, and        mvLXA₁ are derived as follows:

For the derivation of availableFlagB₁, refldxLXB₁, predFlagLXB₁, andmvLXB₁ the following applies:

-   -   The luma location (xNbB₁, yNbB₁) inside the neighbouring luma        coding block is set equal to (xPb+nPbW−1, yPb−1).    -   The availability derivation process for a prediction block as        specified in clause 6.4.2 is invoked with the luma location        (xCb, yCb), the current luma coding block size nCbS, the luma        prediction block location (xPb, yPb), the luma prediction block        width nPbW, the luma prediction block height nPbH, the luma        location (xNbB₁, yNbB₁), and the partition index partIdx as        inputs, and the output is assigned to the prediction block        availability flag availableB₁.    -   When one or more of the following conditions are true,        availableB₁ is set equal to FALSE:    -   xPb>>Log 2XParMrgLevel is equal to xNbB₁>>Log 2XParMrgLevel and        yPb>>Log 2YParMrgLevel is equal to yNbB₁>>Log 2YParMrgLevel.    -   PartMode of the current prediction unit is equal to PART_2N×N,        PART_2NxnU, or PART_2NxnD, and partIdx is equal to 1.    -   The variables availableFlagB₁, refldxLXB₁, predFlagLXB₁, and        mvLXB₁ are derived as follows:

For the derivation of availableFlagB₀, refldxLXB₀, predFlagLXB₀, andmvLXB₀ the following applies:

-   -   The luma location (xNbB₀, yNbB₀) inside the neighbouring luma        coding block is set equal to (xPb+nPbW, yPb−1).    -   The availability derivation process for a prediction block as        specified in clause 6.4.2 is invoked with the luma location        (xCb, yCb), the current luma coding block size nCbS, the luma        prediction block location (xPb, yPb), the luma prediction block        width nPbW, the luma prediction block height nPbH, the luma        location (xNbB₀, yNbB₀), and the partition index partIdx as        inputs, and the output is assigned to the prediction block        availability flag availableB₀.    -   When xPb>>Log 2XParMrgLevel is equal to xNbB₀>>Log 2XParMrgLevel        and yPb>>Log 2YParMrgLevel is equal to yNbB₀>>Log 2YParMrgLevel,        availableB₀ is set equal to FALSE.    -   The variables availableFlagB₀, refldxLXB₀, predFlagLXB₀, and        mvLXB₀ are derived as follows:

For the derivation of availableFlagA₀, refIdxLXA₀, predFlagLXA₀, andmvLXA₀ the following applies:

-   -   The luma location (xNbA₀, yNbA₀) inside the neighbouring luma        coding block is set equal to (xPb−1, yPb+nPbH).    -   The availability derivation process for a prediction block as        specified in clause 6.4.2 is invoked with the luma location        (xCb, yCb), the current luma coding block size nCbS, the luma        prediction block location (xPb, yPb), the luma prediction block        width nPbW, the luma prediction block height nPbH, the luma        location (xNbA₀, yNbA₀), and the partition index partIdx as        inputs, and the output is assigned to the prediction block        availability flag availableA₀.    -   When xPb>>Log 2XParMrgLevel is equal to xNbA₀>>Log 2XParMrgLevel        and yPb>>Log 2YParMrgLevel is equal to yA₀>>Log 2YParMrgLevel,        availableA₀ is set equal to FALSE.    -   The variables availableFlagA₀, refIdxLXA₀, predFlagLXA₀, and        mvLXA₀ are derived as follows:

For the derivation of availableFlagB₂, refIdxLXB₂, predFlagLXB₂, andmvLXB₂ the following applies:

-   -   The luma location (xNbB₂, yNbB₂) inside the neighbouring luma        coding block is set equal to (xPb−1, yPb−1).    -   The availability derivation process for a prediction block as        specified in clause 6.4.2 is invoked with the luma location        (xCb, yCb), the current luma coding block size nCbS, the luma        prediction block location (xPb, yPb), the luma prediction block        width nPbW, the luma prediction block height nPbH, the luma        location (xNbB₂, yNbB₂), and the partition index partIdx as        inputs, and the output is assigned to the prediction block        availability flag availableB₂.    -   When xPb>>Log 2XParMrgLevel is equal to xNbB₂>>Log 2XParMrgLevel        and yPb>>Log 2YParMrgLevel is equal to yNbB₂>>Log 2YParMrgLevel,        availableB₂ is set equal to FALSE.    -   The variables availableFlagB₂, refIdxLXB₂, predFlagLXB₂, and        mvLXB₂ are derived as follows: . . .

FIG. 27 is a block diagram of a video processing apparatus 2700. Theapparatus 2700 may be used to implement one or more of the methodsdescribed herein. The apparatus 2700 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 2700 may include one or more processors 2702, one or morememories 2704 and video processing hardware 2706. The processor(s) 2702may be configured to implement one or more methods described in thepresent document. The memory (memories) 2704 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 2706 may be used to implement, inhardware circuitry, some techniques described in the present document.

FIG. 28 is a flowchart for a video decoding method 2800. The method 2800includes decoding (2802) a video bitstream in which at least one videoblock is represented using a motion estimation region that is dependenton a coding characteristic of the video block, and reconstructing(2804), from the parsing, a decoded version of the video block, whereinthe motion estimation region represents a portion of a video frame thatincludes the video block such that a motion vector merge candidate listscan be independently derived by checking whether a candidate block islocated in that merge estimation region.

In some embodiments, the coding characteristics of the video block mayinclude its partition type (e.g., CU or PU) or may include its shape(e.g., square, tall rectangular or broad rectangular). In someembodiments, the coding characteristic of the video block comprises abit field in the video bitstream, wherein the bit field is in a sequenceparameter set or a picture parameter set or a slice header of the videobitstream. In case that the video block is rectangular, the bitstreammay include two separate fields for horizontal and vertical dimensionsof the rectangular video block.

In some embodiments, the video bitstream may include at least one blockindicated by a parent node that is split into M sub-blocks indicated bychild notes wherein mode information of each sub-block is codedseparately and the M sub-blocks are not further split, and M is aninteger greater than 1, and wherein not all of the M sub-blocks sharesame motion information. Other example embodiments are described in thepresent document, e.g., in the Examples section 3.

FIG. 29 is a flowchart for an example video decoding method 2900. Themethod 2900 includes generating (2902), for a motion compensated videoblock in a video bitstream, a list of merge candidates, according to afirst rule, determining (2904), using a second rule, a current motioninformation from the list of merge candidates, and reconstructing (2906)the video block based on the current motion information.

In some embodiments, the list of merge candidates includes at least onevirtual merge candidate, and wherein the method further includesderiving the at least one virtual merge candidate by scaling motionvectors of another merge candidate to a different reference picture. Insome embodiments, the list of merge candidates includes multiple virtualmerge candidates and the method may then include deriving the multiplevirtual merge candidates by scaling motion vectors of other mergecandidates to different reference pictures. Virtual merge candidates mayinclude, for example, merge candidates that are not directly based oncandidates and motion vectors of spatially or temporally neighboringblocks, but are derived therefrom.

As previously described in Section 3, the derivation of the multiplemerge candidates may be a function on the list of the merge candidates.In some embodiments, scaling of motion vectors may be performed bydetermining scaling amount based on reference picture index.Alternatively, or in addition, quality of picture such as quantizationlevel with which the reference picture was coded, may be used to decidedamount of scaling to be used. For example, reference pictures with lowerquality (e.g., higher quantization) may be de-emphasized by scaling. Insome embodiments, the virtual merge candidates may be added to the listin an order before the temporal motion vector predication candidates.Alternatively, the virtual merge candidates may be added after temporalmerge candidates, but before bi-predictive merge candidates.

FIG. 30 is a flowchart for a video decoding method 3000. The method 3000includes generating (3002), for a video block in a video bitstream, alist of merge candidates, according to a first rule, extending (3004),using a second rule, the list of merge candidates to an extended list ofmerge candidates that includes additional merge candidates, andreconstructing (3006) the video block using the extended list of mergecandidates.

In some embodiments, the extended list of merge candidates includessub-block motion candidates obtained from a block identified by a motionvector of a spatial merge candidate and relative positions between thevideo block and the block. In some embodiments, the extended list ofmerge candidates includes a sub-block merge candidate for an intra blockcopy-coded merge or an affine merge within a current video frame thatincludes the video block.

In some embodiments, the method 3000 may further include derivingmultiple temporal motion vector prediction candidates for the extendedlist of merge candidates using multiple blocks from one or morepictures. The multiple temporal motion vector prediction candidatesinclude at least one candidate that uses a block with a same relativeposition to a top-left of a co-located picture as the video block.Various examples are show, for example, in FIGS. 26A to 26E.

In some embodiments, the method 3000 may further include applying a fullpruning process to the additional merge candidates, wherein the fullpruning process includes checking a new additional merge candidate withall other candidates in the list of merge candidates. In someembodiments, the method 3000 may further include applying a partialpruning process to the additional merge candidates, wherein the partialpruning process includes checking a new additional merge candidate withless than all candidates in the list of merge candidates.

Additional features and variations of the methods 2800, 2900 and 3000are further described in Section 3 of the present document.

In some embodiments, a method of decoding a video bitstream includesparsing the video bitstream, and reconstructing video pictures from theparsing. The video bitstream includes at least one block indicated by aparent node that is split into M sub-blocks indicated by child nodeswherein mode information of each sub-block is coded separately and the Msub-blocks are not further split, and M is an integer greater than 1,and wherein not all of the M sub-blocks share same motion information.The use of such a video coding technique for block based video coding isfurther described throughout the present document.

In some embodiments, the above-described methods may be implemented by avideo decoder apparatus, e.g., the apparatus 2700.

In some embodiments, a video encoder may implement the above-describedduring video reconstruction or motion compensation loop of videoencoding process.

In some embodiments, the above-described methods may be embodied intoprocessor-executable code and stored on a computer-readable programmedium such as one or more memories or an optical storage device or asolid-state drive, and so on.

FIG. 31 is a flowchart representation for a video encoding method 3100in accordance with the disclosed technology. The method 3100 includes,at operation 3102, splitting a block of video data into M sub-blocksaccording to a partition structure. M is an integer greater than 1(M>1). The method 3100 includes, at operation 3104, coding a firstsubset of the M sub-blocks according to common motion information. Themethod 3100 also includes, at operation 3106, coding a second subset ofthe M sub-blocks according to motion information that is different thanthe common motion information for the first subset.

In some embodiments, the partition structure includes a quadtreepartitioning structure in which each parent block includes four childsub-blocks. In some embodiments, the partition structure includes abinary tree partitioning structure in which each parent block includestwo symmetric child sub-blocks. In some embodiments, the partitionstructure includes an asymmetric binary tree partitioning structure inwhich each parent block includes two asymmetric child sub-blocks. Insome embodiments, the partition structure includes a ternary treepartitioning structure in which each parent block includes three childsub-blocks. In some embodiments, a sub-block of the M sub-blocks is aleaf node that is not further split, and wherein the sub-block isconsidered as a coding block.

In some embodiments, the first subset of the M sub-blocks includes firstM-1 sub-blocks in the block of video data. In some embodiments, thesecond subset of the M sub-blocks includes a last sub-block in the blockof video data.

In some embodiments, the second subset of the M sub-blocks is coded witha merge mode. The method 3100 further includes refraining from signalinga merge index of the merge mode in the bitstream upon determining thatthe merge index corresponds to motion information of a neighboring blockof the block of video data. The neighboring block is covered by one ormore sub-blocks in the first subset of the M sub-blocks.

In some embodiments, the second subset of the M sub-blocks is coded witha merge mode. The method 3100 further includes removing a mergecandidate that provides the common motion information for the firstsubset of the M sub-blocks from a merge candidate list of the mergemode.

In some embodiments, the second subset of the M sub-blocks is coded withan advanced motion vector prediction (AMVP) mode. The method 3100further includes refraining from signaling an AMVP motion vectorpredictor candidate index in the video bitstream upon determining thatthe AMVP motion vector predicator candidate index corresponds to motioninformation of a neighboring block of the block of video data. Theneighboring block is covered by one or more sub-blocks in the firstsubset of the M sub-blocks.

In some embodiments, the second subset of the M sub-blocks is coded witha decoder-side motion vector mode or a frame rate up conversion mode.The method 3100 further includes skipping cost calculation for motioninformation that is identical to the common motion information for thefirst subset of the M sub-blocks. In some embodiments, the method 3100also includes determining a cost value associated with the costcalculation to be a maximum value.

FIG. 32 is a flowchart representation of a video decoding method 3200 inaccordance with the disclosed technology. The method 3200 includes, atoperation 3202, parsing the video bitstream. The method 3200 alsoincludes, at operation 3204, reconstructing video pictures based on theparsed video bitstream. The video bitstream includes at least a block ofvideo data that is split into M sub-blocks according to a partitionstructure. M is an integer greater than 1 (M>1). A first subset of the Msub-blocks is coded according to common motion information and a secondsubset of the M sub-blocks is coded according to motion informationdifferent than the common motion information.

In some embodiments, the partition structure includes a quadtreepartitioning structure in which each parent block includes four childsub-blocks. In some embodiments, the partition structure includes abinary tree partitioning structure in which each parent block includestwo symmetric child sub-blocks. In some embodiments, the partitionstructure includes an asymmetric binary tree partitioning structure inwhich each parent block includes two asymmetric child sub-blocks. Insome embodiments, the partition structure includes a ternary treepartitioning structure in which each parent block includes three childsub-blocks. In some embodiments, a sub-block of the M sub-blocks is aleaf node that is not further split, and wherein the sub-block isconsidered as a coding block.

In some embodiments, the first subset of the M sub-blocks includes firstM-1 sub-blocks in the block of video data. In some embodiments, thesecond subset of the M sub-blocks includes a last sub-block in the blockof video data.

In some embodiments, the second subset of the M sub-blocks is coded witha merge mode. A merge index corresponding to motion information of aneighboring block of the block of video data is skipped and theneighboring block is covered by one or more sub-blocks in the firstsubset of the M sub-blocks.

In some embodiments, the second subset of the M sub-blocks is coded witha merge mode. A merge candidate providing the common motion informationfor the first subset of the M sub-blocks is removed from a mergecandidate list of the merge mode.

In some embodiments, the second subset of the M sub-blocks is coded withan advanced motion vector prediction (AMVP) mode. An AMVP motion vectorpredictor candidate index corresponding to motion information of aneighboring block of the block of video data is skipped and theneighboring block is covered by one or more sub-blocks in the firstsubset of the M sub-blocks.

In some embodiments, the second subset of the M sub-blocks is coded witha decoder-side motion vector mode or a frame rate up conversion mode. Acost value associated with motion information that is identical to thecommon motion information for the first subset of the M sub-blocks isdetermined to be a maximum value.

FIG. 33 is a flowchart representation of a video encoding or decodingmethod 3300 in accordance with the disclosed technology. The method 3300includes, at operation 3302, deriving a merge candidate list for a childnode based on a plurality of neighboring blocks of a parent node of thechild node. The parent node represents a unit of video data and is splitinto multiple child nodes according to a partition structure. Themultiple child nodes include the child node and at least another childnode adjacent to the child node. The method 3300 also includes, atoperation 3304, performing a conversion between the unit of video dataand the video bitstream.

In some embodiments, the partition structure includes binary treepartitioning structure in which each parent node includes two symmetricchild nodes. In some embodiments, the partition structure includes anasymmetric binary tree partitioning structure in which each parent nodeincludes two asymmetric child nodes. In some embodiments, the partitionstructure includes a ternary tree partitioning structure in which eachparent node includes three child nodes. In some embodiments, thepartition structure includes a quadtree partitioning structure in whicheach parent node includes four child nodes. In some embodiments, eachchild node is a leaf node that is considered as a coding unit.

In some embodiments, the plurality of neighboring blocks is determinedby selecting a set of allowed blocks by excluding any blocks within theparent node. In some embodiments, the plurality of neighboring blocksincludes one or more replacement blocks to replace the excluded blocks.In some embodiments, the deriving the merge candidate list includescombining the one or more replacement blocks with the set of allowedblocks to obtain the plurality of neighboring blocks.

FIG. 34 is a flowchart representation of a video processing method 3400in accordance with the disclosed technology. The method 3400 includes,at operation 3402, determining a dimension of a motion estimation regionbased on a coding characteristic of a video block. The method 3400includes, at operation 3404, performing a conversion between the videoblock and a video bitstream based on the motion estimation region. Themotion estimation region represents a portion of a video frame thatincludes the video block such that a motion vector candidate list isindependently derived by checking whether a candidate block is locatedin the merge estimation region.

In some embodiments, the coding characteristic of the video blockincludes a partition type. The partition type can be a binary treepartitioning type in which each parent node includes two child nodes.The partition type can be a ternary tree partitioning type in which eachparent node includes three child nodes. The partition type can also be aquadtree partitioning type in which each parent block includes fourchild sub-blocks.

In some embodiments, the coding characteristic of the video blockincludes a dimension of the video block. The coding characteristic ofthe video block may also include a shape of the video block or atemporal layer index indicating a temporal layer of a current pictureassociated with the video block. In some embodiments, the motionestimation region has a width of M and a height of N, M being differentthan N.

In some embodiments, the dimension of the motion estimation region iscoded in the bitstream. The dimension of the motion estimation regioncan be coded in a sequence parameter set, a picture parameter set, or aslice header. In some implementations, the bitstream includes two syntaxelements to indicate a width and a height of the motion estimationregion. In some implementations, the bitstream includes two separateindications of a width and a height of the motion estimation region. Insome implementations, the bitstream includes a flag indicating whetherthe two syntax elements or two separate indications share a same value.

FIG. 35 is a flowchart representation of a video processing method 3500in accordance with the disclosed technology. The method 3500 includes,at operation 3502, deriving multiple temporal motion vector prediction(TMVP) candidates for a video block in a current picture based onmultiple blocks in one or more pictures that are temporally co-locatedwith the current picture. The current picture is excluded from the oneor more pictures. The method 3500 includes, at operation 3502, addingthe multiple TMVP candidates to a motion candidate list associated withthe video block. The method 3500 also includes, at operation 3504,performing a conversion between the video block and a bitstream.

In some embodiments, the one or more pictures includes a single pictureco-located with the current picture. In some embodiments, the multipleblocks are located inside a second block that is temporally collocatedwith the video block. The second block has a same size as the videoblock, and a relative position of the second block to a top-left cornerof a second picture of the one or more pictures is same as that of thevideo block to a top-left corner of the current picture. In someembodiments, the multiple blocks are located inside a coding tree blockcovering a second block that is temporally collocated with the videoblock. In some embodiments, the multiple blocks are located outside asecond block that is temporally collocated with the video block. In someembodiments, the multiple blocks are located outside a coding tree blockcovering a second block that is temporally collocated with the videoblock.

In some embodiments, the second block is identified by a non-zero motionvector. In some embodiments, the non-zero motion vector is derived froma spatial merge candidate of the second block. In some embodiments, thenon-zero motion vector is derived by scaling a motion vector based onone of the one or more pictures.

In some embodiments, the method also includes adjusting one of the oneor more pictures to be a reference picture associated with a spatialmerge candidate. In some embodiments, the second block is identified bya motion vector derived from a merge candidate of the video block. Insome embodiments, the second block is identified by a motion vectorderived from motion information of a spatial neighboring block of thevideo block.

In some embodiments, the method further includes comparing a new TMVPcandidate against all existing TMVP candidates, determining that the newTMVP candidate is identical to an existing TMVP candidate, andrefraining from adding the new TMVP candidate to the multiple TMVPcandidate. Alternatively, the method includes comparing a new TMVPcandidate against a subset of existing TMVP candidates, determining thatthe new TMVP candidate is identical to an existing TMVP candidate, andrefraining from adding the new TMVP candidate to the multiple TMVPcandidate.

FIG. 36 is a flowchart representation of a video processing method 3600in accordance with the disclosed technology. The method 3600 includes,at operation 3602, generating, for a conversion between a video block ina video picture and a bitstream representation of the video block, alist of merge candidates for the video block. The list of mergecandidates includes at least a first merge candidate that is a virtualmerge candidate derived by modifying a motion vector and/or a referencepicture of a second merge candidate. The method 3600 includes, atoperation 3604, performing, using the list of merge candidates, theconversion between the video block and the video bitstream.

In some embodiments, the virtual merge candidate inherits a predictiondirection from the second merge candidate. In some embodiments, thesecond merge candidate is derived using a bi-prediction in which tworeference picture lists are used, and wherein the virtual mergecandidate is derived by modifying motion information associated only oneof the two reference picture lists. In some embodiments, for a firstreference picture list of the two reference picture lists, the virtualmerge candidate inherits a first reference picture associated with thesecond merge candidate that is in the first reference picture list. Insome embodiments, for a second reference picture list of the tworeference picture lists, the virtual merge candidate is derived byscaling a motion vector with respect to a second reference picture thatis in the second reference picture list. In some embodiments, the secondmerge candidate is derived using a uni-prediction in which only onereference picture list is used, and wherein the virtual merge candidateuses a bi-prediction in which two reference picture lists are used.

In some embodiments, the list of merge candidates includes multiplevirtual merge candidates derived based on multiple corresponding mergecandidates. In some embodiments, the method includes selecting, based ona first criterion, one or more merge candidates for deriving the virtualmerge candidate. In some embodiments, the first criterion includes atleast one of: an insertion order of the one or more merge candidatesinto the list; whether a merge candidate corresponds to bi-prediction; atype of a merge candidate, wherein the type indicates whether the mergecandidate is a spatial merge candidate, a temporal merge candidate, acombined bi-prediction merge candidate, a zero motion vector mergecandidate, or a sub-block merge candidate; a coded mode of a mergecandidate, wherein the coded mode indicates whether the merge candidateis coded using affine motion, non-affine motion, illuminationcompensation, or non-illumination compensation; a size of the videoblock; a shape of the video block; or a coding mode of a neighboringblock.

In some embodiments, the method includes selecting one or more spatialmerge candidates for deriving the virtual merge candidate. In someembodiments, the method includes selecting one or more merge candidatescoded using non-affine motion or non-illumination compensation forderiving the virtual merge candidate.

In some embodiments, the method includes selecting, based on a secondcriterion, one or more reference pictures for deriving the virtual mergecandidate. In some embodiments, the second criterion includes at leastone of an index of a reference picture; a picture order count differentbetween a first reference picture and a second reference pictureassociated with the second merge candidate; a quantization parameterdifferent between the first reference picture and the second referencepicture associated with the second merge candidate; or a number oftemporal layers of a reference picture.

In some embodiments, the virtual merge candidate is placed at a firstposition in the list of merge candidate list. In some embodiments, thefirst position includes one of: before temporal motion vector prediction(TMVP) candidates, after TMVP candidates and before combinedbi-predictive merge candidates, or after combined bi-predictive mergecandidates. In some embodiments, a bi-prediction based merge candidatehas a higher priority than a uni-prediction based merge candidate.

In some embodiments, the virtual merge candidate is derived by modifyingthe motion vector of the second merge candidate based on multiplereference pictures, and the multiple reference pictures are ordered by athird criterion. In some embodiments, the third criterion includes atleast one of: an increasing order of a reference picture index; asequential order of checking pictures in different picture lists; aninterleaved order of checking pictures in different picture lists; or acombination thereof.

In some embodiments, the virtual merge candidate includes more than tworeference blocks. In some embodiments, the method includes comparing thesub-block motion candidate against at least a subset of existingcandidates, determining that the sub-block motion candidate is identicalto an existing candidate, and refraining from adding the sub-blockmotion candidate to a list of merge candidates.

FIG. 37 is a flowchart representation of a video processing method 3700in accordance with the disclosed technology. The method 3700 includes,at operation 3702, determining, for a sub-block of a current videoblock, a sub-block motion candidate based on a first block identified bya motion vector of a spatial merge candidate of the current video blockand a relative position between the current video block and a secondblock wherein the spatial merge candidate is from. The method 3700includes, at operation 3704, performing, using the sub-block motioncandidate, a conversion between the current video block and the videobitstream.

In some embodiments, the sub-block candidate is for alternative temporalmotion vector prediction with the first block in a different picturefrom a current picture of the current video block. In some embodiments,the sub-block motion candidate is for intra block copy (IBC) merge modecoding with the first block being within a current frame of the currentvideo block. In some embodiments, the sub-block candidate is for affinemerge mode coding.

It will be appreciated that the present document discloses severaladditional ways by which merge candidates may be computed in videocoding. Embodiments may benefit from these techniques in terms ofimproving quality of compressed representation of video due to theflexibility and ability to more accurately capture motion or changes invideo pictures during encoding, and conveying the information in abitstream by using a low number of bits.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the scope of the invention. Accordingly, thepresently disclosed technology is not limited except as by the appendedclaims.

The disclosed and other embodiments, modules and the functionaloperations described in this document can be implemented in digitalelectronic circuitry, or in computer software, firmware, or hardware,including the structures disclosed in this document and their structuralequivalents, or in combinations of one or more of them. The disclosedand other embodiments can be implemented as one or more computer programproducts, i.e., one or more modules of computer program instructionsencoded on a computer readable medium for execution by, or to controlthe operation of, data processing apparatus. The computer readablemedium can be a machine-readable storage device, a machine-readablestorage substrate, a memory device, a composition of matter effecting amachine-readable propagated signal, or a combination of one or morethem. The term “data processing apparatus” encompasses all apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal, thatis generated to encode information for transmission to suitable receiverapparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A video processing method, comprising: derivingmultiple temporal motion vector prediction (TMVP) candidates for a videoblock in a current picture based on multiple blocks associated with asecond block in one or more pictures that are temporally before or afterthe current picture, and the second block is collocated with the videoblock, wherein the second block has a same size as the video block, andwherein a relative position of the second block to a top-left corner ofa second picture of the one or more pictures is same as that of thevideo block to a top-left corner of the current picture; adding themultiple TMVP candidates to a motion candidate list associated with thevideo block; and performing a conversion between the video block and abitstream, wherein the multiple blocks are located inside a coding treeblock covering the second block, and wherein the second block isidentified by a non-zero motion vector that is derived from a spatialmerge candidate of the second block, the second block is identified by amotion vector derived from a merge candidate of the video block, or thesecond block is identified by a motion vector derived from motioninformation of a spatial neighboring block of the video block.
 2. Themethod of claim 1, wherein the one or more pictures includes a singlepicture co-located with the current picture.
 3. The method of claim 1,wherein the multiple blocks are located inside the second block.
 4. Themethod of claim 1, wherein the multiple blocks are located outside thesecond block.
 5. The method of claim 1, wherein the non-zero motionvector is derived by scaling a motion vector based on one of the one ormore pictures.
 6. The method of claim 1, further comprising: adjustingone of the one or more pictures to be a reference picture associatedwith a spatial merge candidate.
 7. The method of claim 1, furthercomprising: comparing a new TMVP candidate against all existing TMVPcandidates; determining that the new TMVP candidate is identical to anexisting TMVP candidate; and refraining from adding the new TMVPcandidate to the multiple TMVP candidates.
 8. The method of claim 1,further comprising: comparing a new TMVP candidate against a subset ofexisting TMVP candidates; determining that the new TMVP candidate isidentical to an existing TMVP candidate; and refraining from adding thenew TMVP candidate to the multiple TMVP candidate.
 9. A video encodingapparatus comprising a processor configured to implement a method ofvideo processing, comprising: deriving multiple temporal motion vectorprediction (TMVP) candidates for a video block in a current picturebased on multiple blocks associated with a second block in one or morepictures that are temporally before or after the current picture, andthe second block is temporally collocated with the video block, whereinthe second block has a same size as the video block, and wherein arelative position of the second block to a top-left corner of a secondpicture of the one or more pictures is same as that of the video blockto a top-left corner of the current picture; adding the multiple TMVPcandidates to a motion candidate list associated with the video block;and performing a conversion between the video block and a bitstream,wherein the multiple blocks are located inside a coding tree blockcovering the second block, and wherein the second block is identified bya non-zero motion vector that is derived from a spatial merge candidateof the second block, the second block is identified by a motion vectorderived from a merge candidate of the video block, or the second blockis identified by a motion vector derived from motion information of aspatial neighboring block of the video block.
 10. The apparatus of claim9, wherein the one or more pictures includes a single picture co-locatedwith the current picture.
 11. The apparatus of claim 9, wherein themultiple blocks are located inside the second block.
 12. The apparatusof claim 9, wherein the multiple blocks are located outside the secondblock.
 13. The apparatus of claim 9, wherein the non-zero motion vectoris derived by scaling a motion vector based on one of the one or morepictures.
 14. A video decoding apparatus comprising a processorconfigured to implement a method of video processing, comprising:deriving multiple temporal motion vector prediction (TMVP) candidatesfor a video block in a current picture based on multiple blocksassociated with a second block in one or more pictures that aretemporally before or after the current picture, and the second block iscollocated with the video block, wherein the second block has a samesize as the video block, and wherein a relative position of the secondblock to a top-left corner of a second picture of the one or morepictures is same as that of the video block to a top-left corner of thecurrent picture; adding the multiple TMVP candidates to a motioncandidate list associated with the video block; and performing aconversion between the video block and a bitstream, wherein the multipleblocks are located inside a coding tree block covering the second block,and wherein the second block is identified by a non-zero motion vectorthat is derived from a spatial merge candidate of the second block, thesecond block is identified by a motion vector derived from a mergecandidate of the video block, or the second block is identified by amotion vector derived from motion information of a spatial neighboringblock of the video block.
 15. The apparatus of claim 14, wherein the oneor more pictures includes a single picture co-located with the currentpicture.
 16. The apparatus of claim 14, wherein the multiple blocks arelocated inside the second block.
 17. The apparatus of claim 14, whereinthe multiple blocks are located outside the second block.
 18. Anon-transitory computer-readable program medium having code storedthereupon, the code comprising instructions that, when executed by aprocessor, causing the processor to implement a method of videoprocessing, comprising: deriving multiple temporal motion vectorprediction (TMVP) candidates for a video block in a current picturebased on multiple blocks associated with a second block in one or morepictures that are temporally before or after the current picture, andthe second block is collocated with the video block, wherein the secondblock has a same size as the video block, and wherein a relativeposition of the second block to a top-left corner of a second picture ofthe one or more pictures is same as that of the video block to atop-left corner of the current picture; adding the multiple TMVPcandidates to a motion candidate list associated with the video block;and performing a conversion between the video block and a bitstream,wherein the multiple blocks are located inside a coding tree blockcovering the second block, and wherein the second block is identified bya non-zero motion vector that is derived from a spatial merge candidateof the second block, the second block is identified by a motion vectorderived from a merge candidate of the video block, or the second blockis identified by a motion vector derived from motion information of aspatial neighboring block of the video block.
 19. The non-transitorycomputer-readable program medium of claim 18, wherein the one or morepictures includes a single picture co-located with the current picture.20. The non-transitory computer-readable program medium of claim 18,wherein the multiple blocks are located inside the second block.